Polyamines as Modulators of Salt Tolerance in Rice Cultivars

Abstract

The effect of NaCI on the endogenous levels of diamine, putrescine and polyamines, spermidine and spermine, was studied in the shoot system of salt-tolerant and salt-sensitive lines of rice (Oryza sativa L.) cultivars during three growth stages. Salt stress increased the levels of diamine and polyamine in varying degrees among nine rice cultivars investigated. Salt tolerant AU 1, Co43, and CSC1 were effective in maintaining high concentrations of spermidine and spermine, while the content of putrescine was not significantly altered in all the growth stages when plants were exposed to salinity. The salt sensitivity in rice was associated with excessive accumulation of putrescine and with low levels of spermidine and spermine in the shoot system of salt-sensitive cultivars Co36, CSC2, GR3, IR20, TKM4, and TKM9 under saline condition. One of the possible mechanisms of saline resistance was observed to be due to the highly increased polyamines against the low increase in diamines. Alternatively, the salt sensitivity could be due to high increase of diamines and an incapacity to maintain high levels of polyamines.Polyamines are the newest class of compounds to be considered recently as possible plant growth regulators. Specific information on polyamines in salt-stressed plants is scarce. Polyamines have been shown to inhibit senescence in oat protoplast (3) and in whole leaves ofa number ofplant species (1) and to inhibit stress-induced senescence ofbarley leaf discs through stabilization of thylakoid membranes (19 In contrast to halophytes, nonhalophytes vary more in their ability to control ion uptake and translocation of saline environments. The differences in ion regulation, mainly of Na+ and Cl-, cause specific nutritional imbalance that, together with metabolic reactions, is associated with salt tolerance of the species (1 1). Little is known about the physiological basis of the varietal differences of rice in salt tolerance. There is only limited information on the interrelation between salinity and polyamine metabolism of rice (20).Nine rice cultivars were employed in this study. In our earlier studies, varietal differences in salt tolerance in terms of vegetative shoot growth and yield were tested (13), followed by the studies to identify physiological differences in ion regulation and different facets of metabolism, ultimately accounting for salt tolerance and for changes in organic acid (14), enzymes (15), Chl (16), amino acids (17), and inorganic ions (13,14). Having understood some of the cellular and physiological processes that underlie salt tolerance of rice cultivars, as a part of our studies we have examined the changes in the endogenous levels of polyamines that may serve as markers for different phases of the growth response under NaCl saline conditions. The physiological significance of putrescine, spermidine, and spermine levels is discussed with salt tolerance and salt sensitivity of rice. MATERIALS AND METHODSThe seeds of rice (Oryza sativa L.) cultivars AU 1, Co43, CSC 1 (salt toler...

Constitutively Elevated Levels of Putrescine and Putrescine-Generating Enzymes Correlated with Oxidant Stress Resistance in Conyza bonariensis and Wheat

“…l), which is similar to the findings in rice, in which putrescine levels are not induced by salt stress (Krishnamurthy and Bhagwat, 1989). Conversely, putrescine biosynthesis was induced by many stresses, such as ozone (Langebartels et al, 1991;Scalet et al, 1995;Tuomainen et al, 1996), wounding (Yoza et al, 1996), osmotic stress (Flores and Galston, 1984), heat shock (Roy and Ghosh, 1996), oxygen deficiency (Reggiani et al, 1990), and K+ deficiency (Watson and Malmberg, 1996) in other species.…”

Polyamines: potent modulators of plant responses to stress

“…The role of PAs reported that salt-tolerant rice cultivars had higher level of Spd and Spm whereas salt sensitive cultivars maintained only a high level of Put (Basu & Ghosh 1991). Further measurement of PAs levels in different rice cultivars showed that sensitivity to salt stress in rice was associated with excessive accumulation of Put with low levels of Spd and Spm in the shoot systems of the salt sensitive cultivars under saline conditions (Krishnamurthy & Bhagwat 1989). It was inferred that tolerance to salinity in rice cultivars was due to high content of Spd and Spm and low level of Put.…”

Effects of Osmoprotectants upon NaCl Stress in Rice

“…NaC1-stressed rice (Ouyza sativa L.), for example, accumulates polyamines (Krishnamurthy and Bhagwat, 1989) and Pro (Chou et al, 1991;Alia and Saradhi, 1993). When administered externally, these molecules have been found to protect plants from some of the damage that is caused by drought or excess salinity (Kavi Kishor, 1989;Génard et al, 1991;Krishnamurthy, 1991).…”