| Plants under water stress produce different responses and complex signaling cascade in which polyamines (PAs) and nitric oxide (NO) are the most widely studied signals, due to their core value in signal crosstalk. Preliminary work indicates that the abscisic acid (ABA) induced grass pea toxins β-N-oxalyl-L-a, β-diaminopropionic acid,(β-ODAP) and its accumulation significantly correlated with spermine (Spm), and can induce NO in different plant tissues. In this study, pot-culture experiments with soil medium were conducted using grass pea (Lathyrus sativus L.) under controlled-environment conditions to study the exogenous application of Spm and NO on drought tolerance in grass pea. Different parameters including soil water content (SWC), stomatal conductance, leaf relative water content (RWC), plant growth, ABA, β-ODAP content, proline, antioxidant (SOD, POD and CAT), reactive oxygen species (ROS) and MDA were studied. In another experiment we applied different concentration of Spm and NO before flowering and after flowering stage to study the effect on grain yield and related factors affecting on β-ODAP content in grass pea. From this experiment we got the conclusion that Spm and NO can affect the P-ODAP accumulation and other processes that are involved in drought tolerance. The main results obtained from this experimental work are as follows:1. In pot experiment exogenously applied Spm and NO under different drought stress treatments could not enhance the growth parameters such as total biomass, aboveground biomass, stem weight, seeds number, yield, shoot-root ratio, harvest index and the water use efficiency (WUE) in grass pea. Further it is observed that NO showed more inhibitory effect on the plant growth than Spm during water stress treatments.2. Under drought stress, exogenous application of Spm and NO had no significant effect on the increase of β-ODAP in grass pea seedlings, while application of their inhibitors (DFMA and cPTIO) significantly reduce P-ODAP content, indicating that Spm and NO have no direct effect on accumulation of βODAP, although it is essential for its accumulation process. Spm and NO showed no significant difference in all treatment groups under well watered conditions while during moderate and severe drought stress, before flowering and after flowering it markedly improved the β-ODAP content. Although under moderate drought stress, the Spm and NO application before flowering and after flowering stage had no significant difference, while under severe drought stress it showed significant difference after flowering and enhanced the P-ODAP content in seeds.3. During drought stress, exogenously applied Spm and NO caused the delay in appearance of non-hydraulic root signal (nHRS) and hydraulic root source signal (HRS), and significantly enhanced the soil water content (SWC) thresh hold range between the onset of nHRS to the HRS. Comparing with in the control group of drought treatments, Spm and NO application by drench method with two different concentrations (0.1mM and0.05mM) widened the soil water content (SWC) thresh hold range as65.48-36.90%FWC (28.50%FWC) and64.52-33.33%FWC (31.19%FWC) respectively. While application of NO with the same treatment method widened the thresh hold range60-29.71%FWC (30.28%FWC) and63.8-32.86%FWC (30.95%FWC) respectively, comparing with control group that was59.76-41.19%FWC (18.57%FWC).4. Under drought stress, exogenously applied NO and Spm increased the growth of seedlings in grass pea although the effect of NO was more significant than Spm. NO and Spm addition enhanced the content of proline and soluble protein that played significant role during drought stress tolerance. Further the activity of antioxidant, including SOD, POD and CAT improved to scavenge the ROS (production rate of O2-was reduced27.63%) while the content of malondialdehyde (MDA) reduced from2.5ug/g to1.25ug/g.This research work combined the study of different aspects including ecology, physiology and biochemistry and using different research methods, have obtained some new findings. Through different growth stages, various concentrations of Spm and NO had impact on drought tolerance and grass pea toxin synthesis. It showed its inhibitory effect on grass pea yield, biomass and water use efficiency. From seedling experiments it is revealed that the mechanism behind this inhibition is due to Spm and NO application that delayed the onset time of nNHRS and HRS and enhanced the thresh hold range of soil moisture contents (SMC) under drought stress conditions and increasing the drought tolerance in grass pea. Plants regulatory mechanisms was maintained by reducing ROS production ratio, on the other hand enhanced the activity of antioxidant enzymes, so increasing the drought tolerance. Exogenous application of Spm and NO can enhance the drought tolerance and play a significant role to increase the β-ODAP content but do not have any direct effects on this mechanism. |
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