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Aims: We tested here the effect of low nitrogen (N) availability and of UV-C radiations (a physical agent) on the susceptibility of Lactuca sativa L. towards Botrytis cinerea ( BC 87) and Sclerotinia minor ( SM). Methods: We assessed first that a dose of UV-C radiation of 0.85 kJ. m is effective in triggering a positive effect without entailing any negative effect on plants. We then tested the effect of this dose on 62-day-old lettuce plants grown at three N concentrations: 2 (low), 10 (normal) and 20 mM (high). Plants were inoculated 24 h after exposure to UV-C radiation and monitored for 4 days. Results: Analysis of lesion areas showed that leaf susceptibility towards Botrytis cinerea ( BC 87) and Sclerotinia minor ( SM) substantially increased with the increasing N concentrations. Results also showed that the UV-C treatment can reduce MDA and HO concentrations and lesion areas. Reduction of lesion areas reached 67 % on day 4 in the Sclerotinia minor ( SM)-10 mM N trial and 52 % in the Botrytis cinerea ( BC 87)-20 mM N trial. The UV-C treatment also resulted in an increase in the concentration of total phenolics in leaves which could be observed on days 1, 2 and 4 in Sclerotinia minor SM trial and days 1 and 2 in Botrytis cinerea BC 87 trial. Conclusions: Taken together, our observations suggest that UV-C irradiation stimulate the capacity of lettuce plants to resist against Sclerotinia minor (SM) and Botrytis cinerea (BC 87) and that phenolic compounds may be involved in this resistance. [ABSTRACT FROM AUTHOR]

The aim of this research was to examine the effect of UV-C on resistance of lettuce to Botrytis cinerea and Sclerotinia minor. Analysis of the lesion surfaces showed that plants exposed to UV-C were less susceptible to the two pathogens, especially on the fourth day after inoculation. Chlorophyll, carotenoid contents and malondialdehyde and hydrogen peroxide were assayed after 1 day and 4 days. Lettuces treated with UV-C and inoculated showed an increase in chlorophyll and carotenoid content, especially 24 h after inoculation, and low values of the two indicators of oxidative stress as compared with lettuces which were inoculated but did not receive UV-C treatment. [ABSTRACT FROM AUTHOR]

Abstract: The changes observed photosystem I activity of lettuce plants exposed to iron deficiency were investigated. Photooxidation/reduction kinetics of P700 monitored as ΔA 820 in the presence and absence of electron transport inhibitors and acceptors demonstrated that deprivation in iron decreased the population of active photo-oxidizable P700. In the complete absence of iron, the addition of plant inhibitors (DCMU and MV) could not recover the full PSI activity owing to the abolition of a part of P700 centers. In leaves with total iron deprivation (0μM Fe), only 15% of photo-oxidizable P700 remained. In addition, iron deficiency appeared to affect the pool size of NADP+ as shown by the decline in the magnitude of the first phase of the photooxidation kinetics of P700 by FR-light. Concomitantly, chlorophyll content gradually declined with the iron concentration added to culture medium. In addition, pronounced changes were found in chlorophyll fluorescence spectra. Also, the global fluorescence intensity was affected. The above changes led to an increased rate of cyclic electron transport around PSI mainly supported by stromal reductants. [Copyright &y& Elsevier]

Seeds of lettuce, variety Romaine were subjected to different priming treatments such as water, potassium nitrate (KNO3) and gibberellic acid (GA3). Seedlings obtained from primed (Pr) and nonprimed (NP) seeds were grown in a hydroponic culture system supplemented with 0, 100 or 200 mM sodium chloride (NaCl). The different physiological and biochemical responses were studied 15 days after treatment. Under NaCl, the dry weight was higher in plants derived from hydro-primed (HP) seeds when compared to NP, osmoprimed (KNO3P), and hormonal primed (GA3P) ones. Under control and 100 mM NaCl treatment, malondialdehyde (MDA) content and EL did not show any correlation with activities of gaiacol peroxidase (GPX) and catalase (CAT), but did with the increase in reduced ascorbate (AsA) and total ascorbate contents. The results indicated that plants derived from HP seeds exhibited higher adaptive potential under salinity stress. Our findings suggest that a hydropriming technique can be used as a simple commercial approach to alleviate the effects of NaCl induced stress in lettuce plants. [ABSTRACT FROM PUBLISHER]