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Chicory (Cichorium intybus L.) and dandelion (Taraxacum officinale L.) are persistent weeds, the aerial portions of which do not survive in winter. However, subterranean tissues remain viable and facilitate the rapid resumption of growth in early spring. The source of nutrients for growth prior to the establishment of foliage is the roots. Carbohydrate and N reserves are accrued during late summer and autumn, respectively. Hydrolysis of fructans during late autumn occurs coincidentally with increments in sucrose, the latter providing a readily accessible C pool. Nitrate, free amino acids and soluble protein all play substantial roles in nitrogen storage. Asparagine is the predominant amino acid in the free pool during winter, followed by glutamine, ornithine, serine, aspartic acid and glutamic acid. Storage reserves remain at peak levels throughout winter and deeline prior to the resumption of growth. The patterns observed here provide evidence that N is an important currency of storage metabolism and, thus, a framework has been provided for the examination of regulation of N storage in perennial weeds.

During mid-development (25-40 d after pollination: DAP) of the castor bean seed the amount of abscisic acid (ABA) increases in both the endosperm and the embryo, declining substantially thereafter until there is little present in the mature dry (60 DAP) seed. Premature desiccation of the seed at 35 DAP also leads to a major decline in ABA within the embryo and endosperm. Partial water loss from the seed at 35 DAP which, like natural and premature desiccation, leads to subsequent germination upon return of the seed to full hydration, causes a much smaller decline in ABA levels. In contrast, ABA declines substantially in the non-dried (hydrated) control at 35 DAP, but the seeds do not germinate. Hence, a clear negative correlation between ABA content and germinability is not observed. Both drying, whether natural or imposed prematurely, and partial drying decrease the sensitivity of the isolated embryo to exogenous ABA by about 10-fold. The protein synthetic response of the castor bean embryo exposed to 01 mol m"3 ABA following premature desiccation exhibits some similarity to the response of the non-dried developing embryo—in both cases the synthesis of some developmental proteins is enhanced by ABA, and germination is suppressed. Germination of mature seeds is also suppressed by 01 mol m~3 ABA, but the same developmental proteins are not synthesized. In the cotyledons of prematurely-desiccated seed, some proteins are hydrolysed upon imbibition in 01 mol m 3 ABA, a phenomenon that occurs also in the cotyledons of similarly treated mature embryos, but not in developing non-dried embryos. Hence the embryo exhibits an 'intermediate' response upon rehydration in 01 mol m~3 ABA following premature desiccation; viz. some of the responses are developmental and some germinative. Following natural or imposed drying, the isolated embryo becomes relatively insensitive to 0 01 mol rrT 3 ABA: germination is elicited and post-germinative reserve breakdown occurs in the radicle and cotyledons. The reduced sensitivity of the embryo to ABA as a consequence of desiccation may be an important factor in eliciting the switch to germination and growth within the whole seed.

SUMMARY Differential scanning calorimetry and electron spin resonance have been used to characterize the association of gibberellic acid4 and gibberellic acid, (a GA4/GA7 mixture) with phospholipid membranes. The GA4/GA7 mixture lowered the temperature and reduced the co-operativity of the main phase transition of liposomes prepared from dipalmitoylphosphatidylcholine (DPPC), distearylphosphatidylcholine (DSPC) and dipalmitoylphosphatidylglycerol (DPPG), and eliminated the pretransition. The reduction in co-operativity of the main transition was not accompanied by a reduction in transition enthalpy, indicating that the gibberellins simply perturb the bilayer rather than complex with the phospholipid molecules. Perturbation was markedly greater at pH values approaching the pKa of the gibberellin carboxyl group than at pH 7. Moreover, the negatively charged DPPG was less susceptible to perturbation than the zwitterionic phosphatidylcholines. Perturbation by GA8, a physiologically inert gibberellin, was virtually imperceptible. Electron spin resonance of GA4/GA7-treated liposomes of phosphatidylcholine (PC) and phosphatidylglycerol (PG) confirmed the results obtained by differential scanning calorimetry and also indicated that the gibberellins associate with the surface of the phospholipid membranes rather than penetrate into the interior of the bilayer. The data are consistent with the proposal that gibberellins can influence membrane behaviour by modulating the physical properties of the lipid bilayer.

Exposure of leaves to SO2 or bisulfite is known to induce peroxidation of thylakoid lipids and to inhibit photosynthetic electron transport. In the present study, we have examined the temporal relationship between bisulfite-induced thylakoid lipid peroxidation and inhibition of electron transport in an attempt to clarify the primary mechanism of SO2 phytotoxicity. Primary leaves of bean (Phaseolus vulgaris L. cv Kinghorn) were floated on a solution of NaHSO3, and the effects of this treatment on photosynthetic electron transport were determined in vivo by measurements of chlorophyll a fluorescence induction and in vitro by biochemical measurements of the light reactions using isolated thylakoids. Lipid peroxidation in treated leaves was followed by monitoring ethane emission from leaf segments and by measuring changes in fatty acid composition and lipid fluidity in isolated thylakoids. A 1 hour treatment with bisulfite inhibited photosystem II (PSII) activity by 70% without modifying Photosystem I, and this inhibitory effect was not light-dependent. By contrast, lipid peroxidation was not detectable until after the inhibition of PSII and was strongly light dependent. This temporal separation of events together with the differential effect of light suggests that bisulfite-induced inhibition of PSII is not a secondary effect of lipid peroxidation and that bisulfite acts directly on one or more components of PSII.

Phenolics in sugar maple seeds were identified by colour reactions, u.v. spectroscopy and gas-liquid chromatography. Changes in their inhibitory activity during stratification were also followed using several bioassays. p-Coumaric, o-coumaric, and ferulic acids were found in all tissues. The highest concentrations were noted in the embryonic axis and testa, but total amounts per fruit were highest in cotyledons and pericarp. p-Coumaric acid was the principal phenolic in dry seeds, and it declined substantially in all tissues during the first half of stratification with little subsequent change thereafter. Decreases in o-coumaric and ferulic acids per seed were small by comparison, nevertheless losses ranged between 36 and 68% of the original concentrations. Bioassays confirmed that the three endogenous phenolics possessed marked inhibitory properties that diminished with the progress of stratification, but only the compound identified as p-coumaric acid showed major

The growth potential of embryonic axes of Acer saccharum Marsh. increased during moist storage at 5 C but not at 20 C. During the period of increasing growth potential, the oxygen consumption of the axes remained constant. It was possible to distinguish three phases of the stratification-germination process at 5 C with respect to response of the axis to gibberellic acid and kinetin. From 0 to 10 days the growth regulators had no effect on elongation; from 10 to 60 days axis elongation was stimulated; and between day 60 and day 75, when germination had begun, the growth substances were inhibitory. The adenylate energy charge remained low (0.15) in axes of dry dormant seeds but increased to 0.78 following imbibition of water and 10 days of moist storage at 5 C. This phenomenon was not specifically related to low temperature stratification, since a rapid increase in the energy charge of the axes also occurred following imbibition and moist storage at 20 C. The excised axes would elongate in response to the growth substances only when a high energy charge (approximately 0.8) was maintained.

The effects of factorial combinations of N, P and Mg on some of the interrelationships among nutrient ions as they occurred in seedlings of slash pine were investigated. In similar studies, true interactions have not always been differentiated from apparent interactions, the result of comparing foliage concentrations in plants with widely divergent growth rates. To prevent this, nutrient solutions were formulated to produce conditions ranging only from slight deficiency through luxury consumption. This relatively narrow range of nutrition allowed actual interactions to be separated from those changes in foliage concentration that are primarily a result of large differences in growth.The needles were analyzed for total and soluble N and total P, K, Ca, Mg and Na. Each level of each nutrient variable had a significant effect on the concentration of 1 or more dissimilar elements. The familiar depressive effect of N on foliar P was observed; however this relationship was shown to be primarily the result of growth dilution rather than anion antagonism. Increased Mg did antagonistically reduce the uptake of Ca and, generally, K. Increments of P not required for growth stimulated uptake of N, Ca, Mg and K. No relationship was found between Mg supply and P accumulation.