Putrescine transformation to other forms of polyamines in filling grain embryos functioned in enhancing the resistance of maize plants to drought stress.

Polyamines (PAs), one of plant growth regulators, play an important role in the plant resistance to drought stress. However, the precise function of putrescine (Put) transformation to other forms of PAs is not clear in filling maize grain embryos. In this study, two maize (Zea mays L.) cultivars, Yedan No. 13 (drought-resistant) and Xundan No. 22 (drought-sensitive), were used as experimental materials. Maize was planted in big plastic basins during whole growth period, and from the 25th day after fertilization, the plants were treated with drought (-1.0 MPa), PAs and inhibitors for 12 d. The experiments were performed during three consecutive years. The changes in the levels of three main free PAs, Put, spermidine (Spd) and spermine (Spm), covalently conjugated PAs (perchloric acid-soluble), covalently bound PAs (perchloric acid-insoluble), the activities of arginine decarboxylase, S-adenosylmethionine decarboxylase, and transglutaminase were investigated in embryos of filling grains. During drought stress, free Put increased from 109 to 367 nmol g-1 FW and from 107 to 142 nmol g-1 FW in Xundan 22 and in Yedan 13, respectively. Meanwhile, free Spd, free Spm and bound Put increased 2.7, 3.0 and 4.2 times in Yedan 13, respectively, and they merely increased about 1.5 times in Xundan 22. These results suggested that free Spd/Spm and bound Put, which were transformed from free Put, were possibly involved in drought resistance. Exogenous Spd treatment enhanced the drought-induced increase in endogenous free Spd/Spm content in drought-sensitive Xundan 22, coupled with the increase in drought resistance, as judged by the decrease in ear leaf relative plasma membrane permeability and increases in ear leaf relative water content, 1000-grain weight and grain number per ear. The suggestion was further testified with methylglyoxal-bis guanylhydrazone and o-phenanthrolin treatments. Collectively, it could be inferred that transformation of free Put to free Spd/Spm and bound Put in filling grain embryos functioned in enhancing the resistance of maize plants to soil drought.

Polyamines conjugated to plasma membrane functioned in enhancing the tolerance of cucumber seedlings to osmotic stress via elevating H+-ATPase activity.

Polyamine (PA), one of the important plant growth regulators, is closely associated with drought stress. However, the function of conjugated PA is not still clear in the roots of cucumber seedlings under polyethylene glycol (PEG) osmotic stress. Therefore, in this study the relationship between the levels of conjugated polyamines and the activity of H+-ATPase in plasma membrane was elucidated with the roots of two cucumber (Cucumis sativus L.) cultivars, which were different in drought tolerance, as experimental materials. Furthermore, the contents of free PAs and the activities of S-adenosylmethionine decarboxylase (SAMDC) and transglutaminase (TGase), which were closely related to the levels of conjugated polyamines, were also determined. Results showed that under osmotic stress, the increases of the levels of non-covalently conjugated (non-CC) spermidine (Spd) and spermine (Spm), covalently conjugated (CC) putrescine (Put) and Spd in plasma membrane of drought-tolerant Tangshan 5 were more obvious than those of drought-sensitive Jinyou 1. Furthermore, the conjugated PAs mentioned above were closely correlated with increase rate of seedling dry weight, plasma membrane permeability, water content and H+-ATPase activity in plasma membrane. Results of the additional tests, in which exogenous Spd, Spm and two inhibitors, MGBG and phenanthrolin were used, were complementary to the results above. From these results, it could be concluded that non-CC Spd and Spm, CC Put and Spd in plasma membrane functioned in enhancing the tolerance of cucumber seedlings to osmotic stress via elevating H+-ATPase activity.

Conjugated Polyamines in Root Plasma Membrane Enhanced the Tolerance of Plum Seedling to Osmotic Stress by Stabilizing Membrane Structure and Therefore Elevating H+-ATPase Activity.

Polyamines are small positively charged molecules in plants and play important functions in many biological processes under various environmental stresses. One of the most confounding problems relating to polyamines (PAs) in stresses is the lack of understanding of the mechanisms underlying their function(s). Furthermore, a limited number of studies have addressed this issue at the sub-cellular level, especially in tree plants under drought stress. Therefore, in this research, by simulating natural drought stress with polyethylene glycol (PEG) osmotic stress, the relationship between the levels of conjugated polyamines and the activity of H+-ATPase in the plasma membrane was elucidated with the roots of two plum (Prunus salicina L.) cultivars, which were different in drought tolerance, as experimental materials. Furthermore, free PA levels and the activities of S-adenosylmethionine decarboxylase (SAMDC) and transglutaminase (TGase), which were closely associated with the levels of free and conjugated PAs, were also detected. Results showed that under osmotic stress, the increases of the levels of non-covalently conjugated (non-CC) spermidine (Spd) and spermine (Spm), covalently conjugated (CC) putrescine (Put) and Spd in the plasma membrane of drought-tolerant Ganli No. 5 were more significant than those of drought-sensitive Suli No. 3, indicating that these conjugated PAs might be involved in the tolerance of plum seedlings to stress. Furthermore, the conjugated PAs were closely correlated with plum seedling growth, water retention capacity, plasma membrane damage degree, and hydrogen (H+)-ATPase activity in the plasma membrane. To get more complementary pieces of evidence, we subjected plum seedlings to combined treatments of PEG and exogenous PA (Spd and Spm), and an inhibitor of SAMDC [methylglyoxal-bis (guanylhydrazone), (MGBG)] or TGase (o-phenanthroline). These results collectively suggested that non-CC Spd and Spm, CC Put and Spd in plasma membrane might function in enhancing the tolerance of plum seedlings to osmotic stress by stabilizing membrane structure and therefore elevating H+-ATPase activity.