Effect of Exogenous Abscisic Acid on Proline Dehydrogenase Activity in Maize (Zea mays L.)

Abstract

Plant responses to drought stress include proline and abscisic acid (ABA) accumulation. Proline dehydrogenase (PDH) (EC 1.4.3) is the first enzyme in the proline oxidation pathway, and its activity has been shown to decline in response to water stress (PJ Rayapati, CR Stewart [1991] Plant Physiol 95: 787-791). In this investigation, we determined whether ABA treatment affects PDH activity in a manner similar to drought stress in maize (Zea mays L.) seedlings. Four exogenous ABA treatments (0, 11, 33, and 100 micromolar ABA) were applied to well-watered maize seedlings. Mitochondria were isolated and PDH was solubilized using Nonidet P-40. PDH activity was measured by the reduction of lodonitrotetrazolium violet under proline-dependent conditions. There was no effect of ABA on PDH activity at 33 and 100 micromolar ABA, but there was a 38% decline at 11 micromolar. This decline was less than the 69% reduction in activity under drought stress. Endogenous ABA determinations and plant growth rate showed that ABA entered the plant and was affecting metabolic processes. ABA treatments had a small effect on shoot and root proline concentration, whereas drought stress caused a 220% increase in root tissues. We conclude that ABA is not part of the pathway linking drought stress and decreased PDH activity.Plant responses to drought stress include ABA and proline accumulation (1,15). ABA has been shown to induce stomatal closure (9), as well as the transcription and translation of many ABA-responsive genes (1 1). Many of these genes are responsive to both water stress and endogenous ABA level (11 and references therein). The concurrent accumulation of proline and endogenous ABA in response to drought stress has resulted in speculation that ABA may trigger proline increases (12). However, Stewart and Voetberg (14) reported that ABA and proline accumulation were not necessarily linked in leaves of a wilty tomato (Lycopersiconflacca Mill.) This suggests that proline accumulation in response to drought stress may be independent of endogenous ABA levels in some species (14).For proline to accumulate, either synthesis from glutamic acid must be enhanced or the rate of oxidation must decrease, or both. PDH2 is the first enzyme in the proline oxidation Supported by U.S. Department of Agriculture 2 Abbreviations: PDH, proline dehydrogenase (EC 1.4.3); ddH20, distilled water. pathway (4). Recently, Rayapati and Stewart (10) reported the solubilization of PDH from maize (Zea mays L.) mitochondria. It was shown that extractable PDH activity was 10-fold lower in drought-stressed plants compared with wellwatered controls. The objective of the current investigation was to determine whether ABA caused a decline in extractable PDH in a manner similar to drought stress. We report that ABA does not affect extractable PDH activity in well-watered maize seedlings. MATERIALS AND METHODSMaize seedlings (Zea mays L. cv B73) were grown in the dark in vegetable crispers containing vermiculite at 30°C. The effects on PDH activity of fo...

Exogenously applied ABA induced changes in physio-biochemical attributes in selected rice varieties under osmotic stress

“…According to Shevyakova et al (2013), ABA suppressed PDH activity when treated to the roots. Dallmier and Stewart (1992) also stated that exogenous ABA declines PDH activity, which is very small, compared to level declined in response to drought stress suggesting that ABA is not the pathway linking drought stress and PDH activity. In our experiment, no response of ABA was observed on PDH activity.…”

Proline Accumulation in Maize (Zea mays L.) Primary Roots at Low Water Potentials (I. Requirement for Increased Levels of Abscisic Acid)

“…Evidence in other systems shows that both Pro synthesis and oxidation can be affected at low J/w as a result of changes in enzyme activities and their gene expression (Delauney and Verma, 1993). The small amount of published information on the effects of ABA on these processes shows that exogenously supplied ABA can increase conversion of glutamate to Pro in barley leaves (Stewart, 1980) and inhibit Pro dehydrogenase activity in maize seedling shoots (Dallmier and Stewart, 1992). Experiments to understand how low $w and endogenous ABA manipulation affect the rate of Pro deposition in the root growth zone at low $w are in progress and will be reported in a subsequent paper in this series.…”

Effect of osmotic stress and sodium nitroprusside pretreatment on proline metabolism of wheat seedlings

“…Uchida et al (2002) also found that the expression of P5CS was increased in response to NO in rice seedling leaves under salinity conditions, which could confer increased tolerance to salt stress. Moreover, many previous studies reported that the abscisic acid (ABA) was proposed to promote proline accumulation in response to a variety of environmental stresses (Dallier and Stewart 1992, Hare et al 1999, Zhang et al 2005. Ruan et al (2004) showed that NO could activate the synthesis of endogenous ABA in wheat seedling leaves under 150 mM NaCl salt stress, which was in agreement with the results of Zhao et al (2001) that the synthesis of ABA was inhibited by nitric oxide synthase (NOS) inhibitors in responding to drought stress.…”