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The extent to which crops are adapted to specific environments greatly depends on how their development is affected by climatic factors. Development in bambara groundnut ( Vigna subterranea (L.) Verdc.) is known to be influenced by temperature and photoperiod. The objective of this study was to quantify the influence of these factors on reproductive development in selections from different origins.Models relating development rates to photoperiod and temperature with linear equations were made for different bambara groundnut selections on the basis of research in semi-controlled environments. The photoperiod and temperature responses could be explained very well by the photothermal conditions in the regions where the selections were obtained. Validation of the models with the results of glasshouse and field experiments showed good to reasonable agreement between observed and predicted times to flowering and podding.It is shown that the average photoperiod between flowering and podding determines the rate from flowering to podding, and that a gradual increase or decrease in photoperiod does not affect that rate. This means that photothermal models intended to predict bambara groundnut development in field situations with fluctuating photoperiods can be based on studies with constant photoperiods. It is also shown that growth and development in bambara groundnut are largely independent and that there are no strong direct photoperiod effects on dry matter partitioning.The usefulness of photothermal development models for identifying suitable selections for different locations and sowing dates is demonstrated in a simulation study for Botswana. It is concluded that the influence of photoperiod and temperature on bambara groundnut development can be quantified through descriptive linear models, using data from semi-controlled environment experiments with constant temperatures and photoperiods. These quantitative models, either on their own or incorporated into a crop growth model, can be useful instruments for matching bambara groundnut genotypes and specific environments.

Vegetable oils are an important commodity world-wide with an annual production of about 70 million tonnes. Oilseed rape is one of the four major crops, providing about 10% of the total production. Quality of vegetable oils is determined by the fatty acid composition of the triacylglycerols (TAG) that constitute such oils. These fatty acids comprise a range of chain lengths and desaturated and oxidised residues. A small group of fatty acids dominates the edible oils which are the predominant products, whereas other specific types of fatty acids are used in specialised applications and generally occur in small crops and wild species. One of these fatty acids is erucic acid (22:1), a very long chain monounsaturated fatty acid, which naturally occurs in species of the Brassicaceae.Synthesis of all fatty acids requires a group of enzymes, most of which have been isolated from a number of species. After synthesis of the primary fatty acids, palmitic (16:0), stearic (18:0) and oleic acid (18:1), in the plastids, they are exported as their CoA-esters into the cytoplasm, where modification and incorporation in lipids occurs. This requires another group of enzymes, some of which, like desaturases and acyltransferases, have been isolated and characterised but most of the species specific modifying enzymes have not been isolated yet. However, little is known about the mechanisms that regulate and coordinate the expression and activity of these enzymes. This thesis focuses on the accumulation of 22:1 and the regulation of the elongase synthesising this fatty acid from 18:1.It has been reported that 22:1 levels can be influenced by growth temperature (Canvin, 1965) but little was known about the regulatory mechanism and timing of this influence. We compared the accumulation of oil and 22:1 in seeds of different cultivars at two temperatures, 15 and 25°C. It was shown that the level of 22:1 in seeds increases from 30 to 40 mol% with a temperature decrease from 25 to 15°C in only one cultivar, Reston, whereas Gulle was shown to be insensitive to changes in temperature. In these experiments we also showed that growth temperature exerts its effect only during the time of maximum oil synthesis, not before or after.Similar experiments showed that microspore-derived embryos (MDEs), grown in vitro, followed a similar pattern of oil accumulation and timing of temperature influence as described for seeds on the intact plant. However, the absolute levels of oil and 22:1 were much lower in MDEs than in seeds and the fraction 22:1 of total fatty acids was reduced by about 10 mol% in MDEs.Analysis of the levels of abscisic acid (ABA) in developing seeds together with the low levels of this plant growth regulator in MDEs suggested that ABA may be an important factor in determining the level of 22:1 in the oil of oilseed rape. However, dose response curves for ABA in MDEs grown at 15 and 25°C showed that the sensitivity to ABA is not influenced by culture temperature. At both temperatures a 50% response was observed at about 0.3 µM and the increase in 22:1 was about 10 mol% at saturating ABA levels. We also found that ABA levels in seeds are saturating at both temperatures, implying that ABA cannot be an intermediate in the transduction of a temperature signal.In addition, statistical analysis of temperature and ABA effects in MDEs showed no significant interaction between these two stimuli. This was further confirmed by the fact that, absolute amounts of both oil and 22:1 increased upon addition of ABA, whereas with temperature only affected the fraction of 22:1 and not the total amount of oil in MDEs.We also studied the effects of a group of demethyl-ABA analogs. In this study we found that the T-methyl group is very important for ABA activity. Removal of this group resulted in a 100-fold increase in the amount of the (+)-enantiomer needed to induce a similar increase in 22:1 accumulation as compared to natural (+)-ABA while a complete loss of activity was observed for (-)-7'-demethyl-ABA. The function of the 8'and 9'-methyl groups is less clear.Removal of these groups resulted in a partial reduction in ABA activity, but the effects were different for total fresh weight accumulation and 22:1 levels. This suggests that at least two types of ABA receptors operate in MDEs.Changes in 22:1 level in the oil must be caused by changes in the enzyme activities catalysing oil biosynthesis. Holbrook et al. (1992) had already shown that the addition of ABA to culture medium resulted in an increase in elongase activity, but little was known about the effect of temperature on elongase activity. We elaborated on the effects of ABA application on elongase activity in MDEs at two different temperatures, 15 and 25°C. We found higher total elongase activities in MDEs grown at 15°C, but temperature sensitivity and effect of 18:1 -CoA concentration were not affected.The differences in total activity correlated closely with the differences observed in 22:1 amount in the MDEs, suggesting that the amount of 22:1 is regulated by the total amount of elongase activity. The correlation between elongase activity and the fraction 22:1 in the oil was lower and no correlation was found between acyltransferase activity and the amount of oil accumulated. It was not possible to properly determine the kinetic parameters K m and V max of the elongase complex due to rapidly loss of activity upon isolation from the membrane and to substrate inhibition by 18:1-CoA at relatively low concentrations (about 10 µM). This inhibition by 18:1-CoA is apparently caused by a detergent effect of this compound disrupting the membrane in which the elongase complex is embedded.Based on these observations a model was formulated to describe the regulation of 22:1 accumulation and oil composition in oilseed rape. The total amount of oil is regulated by the activity of fatty acid synthase (FAS), synthesising fatty acids from acetyl-CoA, derived from carbohydrates imported into the embryo. The main product of FAS, oleic acid, is exported from the plastid and enters the cytoplasm as 18:1-CoA. The pool of 18:1-CoA is modified by desaturases and elongase transforming part of it into other fatty acids like 18:2 and 22:1.Subsequently, the fatty acids in this pool are incorporated in TAG. The acyltransferases performing two out of three of these reactions have little or no selectivity for the various fatty acids and therefore the fatty acid composition of the oil largely reflects the fatty acid composition of the acyl-CoA pool. The fraction of 22:1 in this pool is determined by the relative activity of the elongase in comparison to the total flux of fatty acids through the pool.With the knowledge that elongase activity regulates the amount of 22:1, it must be possible to increase the level of 22:1 in the oil beyond the level of about 55% observed so far (Scarth et a/., 1995). Selectivity of the second acyltransferase, excluding 22:1 from the sn-2 position of TAG, which would limit the maximum 22:1 level to 67%, has been circumvented by transformation of oilseed rape with an acyltransferase that can incorporate 22:1 at this position (Lassner et al., 1995). Whether it will be possible to increase the level of 22:1 in the oil of oilseed rape up to 90 or 100% of fatty acids, greatly increasing the value of rapeseed oil for industrial purposes, will depend upon the effects of increased 22:1 levels on lipid metabolism.

The kinetics of the chemical reactions of lactose during heat treatment of milk were studied. Skim milk and model solutions resembling milk were heated. Reaction products were determined and the influence of varying lactose, casein and fat concentration on the formation of these products was studied. It was observed that lactose isomerized into lactulose, and subsequently degraded into galactose, formic acid, deoxyribose, hydroxymethylfurfural, furfural and furfuryl alcohol; lactose also reacts with lysine-residues to form lactulosyllysine-residues (early stage of the Maillard reaction). From these results, a model describing the steps in the reaction network of the degradation reactions of lactose during heating of milk was proposed.It was tried to model the degradation of lactose by computer simulation in order to predict the quantities of the various degradation products in the course of time. The model appeared to fit the experimentally obtained results reasonably well. Altogether, the hypothesized mechanism for degradation of lactose appeared adequate to explain the observations for milk and model solutions resembling milk. Mathematical modelling thus allowed rigorous checking of a proposed complicated reaction network in foods. In the case of milk it has been found that, from a quantitative point of view, the isomerization reaction is much more important than the Maillard reaction in the degradation of lactose during heat treatment of milk.

Heat-induced coagulation of concentrated skim milk was studied. Heat-induced changes in partition between serum and colloidal particles of calcium and phosphate and of the various proteins were investigated as a function of heating time and conditions like pH, addition of phosphate and preheating. Aggregation of casein micelles upon heating was assessed by various methods, both at 120°C and after cooling to 20°C. A qualitative model for heat-induced coagulation of concentrated skim milk was proposed, which largely explained phenomena like the effects of pH, addition of phosphate and preheating. For concentrated skim milk produced from preheated milk, this model was also discussed semi-quantitatively. It is shown that the geometry of the emerging aggregates influences time of visible coagulation as much as the rate of aggregation of casein particles.

IntroductionThe international character of the poultry industry requires that poultry bred under temperate conditions should be able to perform under tropical conditions as well. However, abrupt changes in environmental temperature or continuous high temperatures may affect production traits, immune responsiveness, and thus disease resistance.Improved disease resistance can be obtained by breeding for high immune responsiveness. However, if the effects of a stressor, e.g. high temperature, is be different in the successive selection lines, the selective advantage can be lost.Two mechanisms might cause such a genotype x environment interaction. First, the stress susceptibility may be increased after the selection for high responsiveness. Second, the body weight, and thus possibly metabolic rate, may be different between the selection lines. This could imply different thermal requirements of the birds, and thus different reactions to changed environmental temperatures.In the present studies, the effects of acute thermal stress and continuous high temperature on antibody production to sheep red blood cells (SRBC) were investigated in young chickens, which had been selected for either high (H) or low (L) antibody titers to SRBC for several generations. Also, the influence of infused corticosterone, the "stress "hormone that is held responsible for immunosuppression, was studied. The general aim of the studies was to investigate the occurrence of genotype x environment interactions and the causes for such interactions.Chapter ITo study the effects of acute thermal stress on antibody production, three experiments were carried out. The chickens were subjected to an acute heat stress treatment (4 periods of½h at 42°C, with ½ h intervals) 24 h before an immunization with SRBC. Experiments reported in literature described considerable immunosuppressive action of such treatments. This treatment could give therefore a good opportunity to study the possible differences in response between the selection lines.Immunizations were given intramuscularly (i.m.) and intravenously (i.v.) (with different doses). Only in one experiment was a relatively small, but significant, immunosuppressive effect found in the H line, but not in the L line. The immune response in the H line was always considerably higher than in the L line.Chapter IITo quantify the impact of the heat stress treatment on the birds, changes in a number of physiological parameters were studied in the birds, which were subjected to the treatment described in chapter I.During the heat stress treatment cloacal temperature and plasma corticosterone were increased. Changes in numbers of circulating leukocytes, and plasma albumin and fibrinogen concentrations were not changed during the heat stress, but changed during the following days in which the immune response was developing. Differences in these changes between i.m. and i.v. immunized birds were found, but H and L line were not different.Chapter IIIIn chapter III an experiment is described, in which the chickens were placed in climate chambers. In this experiment, an acute thermal stress was given, comparable to that described in chapters I and II, but the effects of prolonged heat on the birds were also studied. After acclimation to high temperature, the influence of acute stress diminishes, and endocrine and metabolic changes can affect antibody production. The environmental temperature was constant either 25° or 35°C or it fluctuated daily between 15-25°C or 25-35°C. At the time the immunization with SRBC was given, some of the chickens were exchanged between the different temperatures (acute stress).At the high temperature, the chickens were hyperthermic, showed depressed growth, and post mortem lower weights of lymphoid organs were found equally in acclimated and non-acclimated chickens. Birds moved from 25° to the 35°C environment (CH) had a lower immune response than those that remained at 25° (CC). The birds which were already in the 35° environment before immunization (HH) mounted higher immune responses. The responses in birds which were kept in the chambers with fluctuating temperatures, showed less pronounced differences, suggesting a smaller impact of these temperatures, or a better acclimation of the birds to the temperature. These effects were the same in H and L line chickens.Chapter IVA number of experiments are described in chapter IV, in which the ontogeny of lymphoid organs (important for the immune system), and the number of plaque-forming-cells (the precursors of the antibodysecreting cells) in the spleen were studied. Aim of this study was to find morphological differences between the H and L line that might determine the difference in immune responsiveness. It was found that the spleen was already heavier in the H line than in the L line, before immunization. Also, higher numbers of plaqueforming-cells were found in the spleen of birds from the H line than in those of L line birds after immunization. These differences contribute to the differences in antibody production after immunization.Chapter VBecause the effects of acute heat stress on antibody production, described in chapters I and III, were smaller than expected, a study with direct application of corticosterone was done. Corticosterone is the hormone presumed to cause immunosuppression after stress. Direct administration of corticosterone might reduce the variability in the response measured after thermal stressors, and thus provide a more precise comparison of stress effects between the lines. In chapter V this experiment is described in which the birds were infused with a corticosterone solution (CS).Major effects of the CS treatment on plasma corticosterone, growth, leukocytes and lymphoid organs were found. The antibody titers to SRBC were unaffected, in the H and L line.In chapters VI, VII and VIII the effects of the treatments already described in chapter III, (CC, HH and CH) and V (CS infusion) were studied more extensively. Changes in metabolic rate, growth, energy and protein turnover, caused by the different temperature treatments might have comparable effects on antibody production as obtained by selection. These treatments were studied in relation to changes in endocrine factors (corticosterone, growth hormone, somatomedine, thyroid hormonesT 3andT 4 )and energy metabolism. Therefore these studies were performed in the climate-respiration chambers.Chapter VIBecause an average weight difference exists between the H and L line (L line is usually about 7% heavier) the influence of differences in metabolic rate between the lines on antibody production was studied.Heat production was recorded at different temperatures in both lines. Heat production was somewhat higher in the L line than in the H line in one of two experiments, but no lower critical temperature could be estimated in either line. Thermo-neutrality was maintained by adjusting feed intake.During the immune response only minor differences in energy metabolism were detected between the two lines. These could not unanimously be related to the height of the immune response.Chapter VIIChickens were subjected to a CC, CH or HH treatment, as described in chapter III. The effects of high temperature on metabolism were very evident. Decreased feed intake, growth rate, heat production and fat deposition were found. In the CH treatment also a decreased protein retention was found during the balance period immediately after the temperature change. Effects on cloacal temperature and lymphoid organs were as reported before (Chapter III). The effects of the temperature treatments on antibody production were not as impressive as found in the experiment in chapter III. Plasma corticosterone and thyroid hormones were not affected, somatomedine was increased and growth hormone decreased in hot environments. Differences in metabolic traits, caused by the different environmental temperatures were not related to differences in antibody titers, and differences in antibody titers between the H and L line were not reflected in differences in metabolic rate.Chapter VIIIFinally, the CC and HH treatments were compared to CS infusion. Some effects of the infused corticosterone and HH treatment were similar. Decreased feed intake, growth and heat production were found in both treatments. Also lymphoid organs were negatively influenced in either treatment. But no increased plasma corticosterone levels were evident in HH treatment.T 4concentration was decreased in CS infused birds;T 3was lower in CS infused and was the lowest in HH treated birds. The energy balance was higher in CS infused birds immediately after immunization. Fat deposition was higher in CS infused birds. A small stimulatory effect of the HH treatment on antibody production was found in the L line birds only. Similar to chapter VII, no clear relations between endocrine parameters, energy metabolism and antibody production were found. It was questioned whether the CS infusion is valuable as an experimental model for continuous (heat) stress, because of the marked differences in a number of the measured characteristics.DiscussionIn the discussion it is argued that the differences between H and L line in antibody production are very steady.IFrom the experiments, it is evident that severe heat stress, prolonged heat and corticosteroids do affect the birds: growth, body temperature, corticosterone and other hormones, lymphoid development are changed, but equally in both lines. The selection did not result in a "high stress susceptibility line".Moreover, both lines are apparently rather stress resistant, with regard to antibody production. Acute heat stress, prolonged severe heat and evencorticosterone infusion could only marginally affect antibody titers. If the antibody production was affected by the experimental treatment, the changes were usually very similar in the H and L line. The absence of genotype x environment (heat stress) effects was therefore apparent.The influence of metabolic rate, as measured here, on antibody production was rather small. Some changes in fat deposition during the balance period immediately after the immunization were found, which could indicate a shift in energy distribution between fat and protein, during the immune response. But no direct relation between metabolic rate, influenced by selection or environmental temperature with endocrine regulation and antibody production was found. It was also concluded therefore that the difference in bodyweight between the selection lines is rather based on linked genes than physiologic meaningful relations between the immune system and energy metabolism.

The influence of temperature in the range 15-22 °C on growth, production, quality and flower bud atrophy ('blindness') of the rose cultivars Sweet Promise and Varlon was studied. The roses were grown in Dutch glasshouse soil under natural light conditions and studied from October until May during 7 successive years. The influence of the distribution of the air temperature between day and night was studied. Besides the usual night-lower-than-day-temperature regime, also the reverse situation was studied. 'Models' were constructed for: bud break, development time from bud break until harvest, shoot and flower bud weight, shoot length, the length, width, volume and freshweight of the flower bud during harvest and the diameter of shoot and neck, in relation to date of bud break and mean daily temperature during shoot growth.Complementary studies including roses of the cv. Sweet Promise grown in transferable containers were performed in glasshouses and in growth rooms (Phytotron). In these experiments the interaction of temperature and shoot stage with the development time of a shoot, with shoot weight and with shoot length was studied. Shoot weight showed a clear interaction with temperature if night temperature was higher than day temperature. Various shoot stages showed a different sensitivity to temperature with respect to the formation of flowerless ('blind') shoots. A low night temperature during the period cut until shoot elongation (=4cm) decreased blindness, but increased blindness when given in the next period until the flower bud is clearly visible. Higher night temperatures than those commonly used increased production by decreasing the percentage of blind shoots.At a given daily mean temperature an increase in night temperature showed no significant influence on bud break and development time of a shoot but fresh shoot weight and shoot length are significantly reduced, if night temperature increases above day temperature. The mean temperature and the mean irradiance during shoot growth could account for 98 % of the variation in the relevant 'models' when analysed by linear regression analysis. Adding the variable 'relative humidity' to the regression equation explained 97 % of the variation in shoot weight. To explain 87 % of shoot length the variable 'Weight of the Parent shoot' and the square of the temperature had also to be introduced.Heavy parent shoots produced heavier daughter shoots than light parent shoots. The difference in fresh weight for daughters of heavy parent shoots compared to those of light shoots decreased in autumn and increased again in spring. If light intensity decreased in autumn, less light was used to produce one gram fresh shoot weight, while under increasing light intensities more light was used.Fresh weight production per shoot per day increased with temperature for the cultivar Varlon and as a consequence, the amount of light needed per gram fresh weight decreased. In the period December until the middle of March 'Sweet Promise' showed another, reversed, situation: fresh weight production decreased with temperature. This was caused by the fact that 'Sweet Promise' was weakened more by a raise in temperature than "Varlon'. Production in number of flowers and in grams fresh weight per shrub showed a positive linear correlation with temperature for both cultivars.The course of bud break and harvest was studied for 9 night/day temperature combination. A lower temperature resulted in delayed bud break and production.The research made it clear that it is possible and profitable to control temperature on the basis of the daily mean temperature or the temperature sum during bud break and shoot growth, instead of in the orthodox way with a fixed night-lower-than-day temperature regime. Practical applications of the results are given for commercial rose growing. Heating glasshouses on a basis of a daily mean temperature or temperature sum instead of a given day and night temperature is a possibility of saving energy, as also is the maintaining of a diurnal period of up till 6 hours with a higher night than day temperature beginning at sunset when the thermal screens are closed.Soil heating until 20 °C did not influence production and quality,whilst a 12% reduction in light had a negative effect on both. De invloed van de kasluchttemperatuur tussen 15 en 22 graden Celsius op de groei, de produktie, de kwaliteit en de loosvorming van de rozencultivars "Sweet Promise" (Sonia) en "Varlon" (Ilona) werd bestudeerd in de periode oktober tot mei in 6 achtereen volgende jaren. De rozen werden geteeld in kasgrond onder natuurlijke licht omstandigheden. Naast de invloed van de gemiddelde etmaaltemperatuur tijdens de groei werd ook de invloed van de temperatuurverdeling tussen dag en nacht bestudeerd. Behalve de gebruikelijke situatie met een lagere nacht- dan dagtemperatuur werd ook de tegenoverstelde situatie met een hogere nachttemperatuur bestudeerd. Groeimodellen werden opgesteld voor de ontwikkelingsduur van de scheut, de lengte, het gewicht, de diameter van de scheut en de bloemknop. Met behulp van de resultaten kan de teeltplanning van kasrozen verbeterd worden