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

Abstract

Previous work showed that the concentration of proline (Pro) increases greatly in the primary root tip of maize (Zea mays 1.) at low water potentials (qw). It was also shown that the maintenance of root elongation at low $ , depends on increased levels of abscisic acid (ABA). In this study we have assessed whether ABA is required for the increase in Pro concentration. Seedlings were grown in vermiculite of various $ , , and endogenous ABA levels were decreased using either fluridone (FLU) or the vp5 mutant to inhibit carotenoid (and ABA) synthesis. In both treatments, Pro concentrations at low qW were substantially decreased throughout the apical centimeter, which encompassed the elongation zone. Pio concentrations in FLU-treated roots were restored by addition of 7 BM ABA to the vermiculite, which raised the interna1 ABA content to the leve1 in untreated roots at the same qW. Pro and water content profiles were combined with published growth-velocity distributions to calculate the distribution of net Pro and water deposition rates using the continuity equation. At a $w of -1.6 MPa, the rate of Pro deposition in the root tip was decreased by 75% in FLUtreated compared to untreated roots. FLU treatment increased root diameter and, therefore, water content per unit length, but water deposition rates decreased due to the dominant influence of reduced longitudinal expansion. Thus, the decrease in Pro concentration was attributable entirely to the decrease in Pro deposition.The results demonstrate that increased ABA is required for high rates of Pro deposition and, thereby, high Pro concentrations in the growing region of maize primary roots at low qW.

Translatable RNA Populations Associated with Maintenance of Primary Root Elongation and Inhibition of Mesocotyl Elongation by Abscisic Acid in Maize Seedlings at Low Water Potentials

“…This increase in activity was suppressed when ABA accumulation and elongation were inhibited by treatment with FLU and could be restored with exogenous ABA. It has also been demonstrated that the accumulation of ABA in the primary root at low i// w is required both for the dramatic increase in Pro concentration that occurs in the apical region (Voetberg and Sharp, 1991;Ober and Sharp, 1994) and for restriction of ethylene synthesis and/or sensitivity . Both effects probably involve control at the level of gene regulation.…”

“…Vermiculite Ilr, values were measured for each experiment by isopiestic thermocouple psychrometry (Boyer and Knipling, 1965). For the FLU treatments, FLU was added at a concentration of 10 p~ to the water mixed with the vermiculite at the time of planting and transplanting (Saab et al, 1990;Ober and Sharp, 1994). Seedlings were then grown in the dark at 29°C and near-saturation humidity.…”

Plant water relations and proline accumulation on two cowpea (Vigna unguiculata (L.) Walp.) cultivars as a response to water stress

“…Earlier studies showed that proline accumulated as a response to a decrease in water potentials (Handa et al, 1986;Ober & Sharp, 1994;Bussis & Heineke, 1998) and or RWC (Rajagopal et al, 1977;Argandona & Pahlich, 1991). This response in proline content caused some osmotic adjustment (Handa et aI., 1986;Bussis & Heineke, 1998), which enabled the plant to re-acquire turgidity under water shortage.…”

“…Proline content has been reported to increase in response to a decrease in water potential (Handa et al, 1986;Ober & Sharp, 1994;Bussis & Heineke, 1998) or RWC (Rajagopal, Balasubramanian & Sinha, 1977;Argandona & Pahlich, 1991). Proline accumulation affects osmotic potential (Bussis & Heineke, 1998) and is therefore regarded as an important criterion for selecting drought tolerant crops (Singh, Aspinall & Paleg, 1972).…”

Genetic Transformation in Conifers

“…In recent years, a number of genes for ion pumps have become available thus opening the door for their genetic ~nallipulatio~~ in plants (Jia et al, 1992;Bohnert et al, 1995). An alte~~late aplxoach to tolerallce of both high salt and osmotic stress is the accumulation of o~ganic oslnolytes and other nretabolites, such as glycerol, arabitol, mannitol, sugars, proline, glyci~ie-betaine, and probably polyamines (Rliodes and Hanson, 1993;Ober and Sharp, 1994;Chiang ant1 Dandekar, 1995;Ye et al, 1997). The biosynthetic pathways for these protlucts have been elucidated, providing a great potential for plant improve~l~ent through genetic engineering (Bartels and Nelson, 1994;lngram ant1 Bartels, 1996).…”