Effects of growth substances on the protoplasmic drought tolerance of leaf cells of the resurrection grass, Sporobolus stapfianus

Abstract

Hydrated leaves of the resurrection grass Sporobolus stapfianus Gandoger are not desiccation tolerant, but moderate to severe drought stress can induce their desiccation tolerance while the leaves remain attached to drying intact plants. Free-cell suspensions prepared from fully turgid leaves of S. stapfianus were also found to be desiccation-sensitive. In this study a sensitive assay was developed to determine the effect of exogenous substances on the protoplasmic drought tolerance (PDT) of cell suspensions. Suspended cells were incubated with a wide variety of individual plant growth substances over a range of concentrations. After the incubation, the protoplasmic drought tolerance at each concentration of each substance was determined osmotically. Brassinolide (BR) and methyljasmonic acid (MJA), applied separately, gave the greatest effect — each improved PDT by approximately 6 MPa, compared with controls incubated without growth substances. Exogenous abscisic acid (ABA) improved the PDT of S. stapfianus only slightly (about 1 MPa). Salicylic acid (SA), 1-aminocyclopropane–1-carboxylic acid (ACC), ethephon, gibberellic acid (GA), kinetin (KN) andN 6 -(2-isopentyl)adenine (2ip) each improved PDT by ca 1.5 MPa. Indoleacetic acid (IAA) had no effect, and zeatin (ZN) had a deleterious effect on PDT. Incubation of suspended cells in combinations of two growth substances (MJA with ABA, ACC, BR, GA, IAA or KN; BR with ABA) produced no evidence of synergism, or in most cases, even of additive effects of the tested substances. ABA, BR and MJA (applied separately) stimulated the synthesis of numerous specific proteins. Each growth substance stimulated the synthesis of differing proteins, with four exceptions. This investigation raises the possibility that BR and MJA may play a role in a chain of events which leads eventually to the induction of desiccation tolerance in leaves of S. stapfianus. The effects on cell PDT observed in this study, while large, were insufficient to account for the remarkable improvement observed in the PDT of S. stapfianus leaves attached to drying plants.

The resurrection plant Sporobolus stapfianus: An unlikely model for engineering enhanced plant biomass?

“…1 The resurrection grass S. stapfianus Gandoger in the hydrated and desiccated state, respectively drought tolerance of S. stapfianus mesophyll cells, methyl jasmonic acid was the most effective. However, the increment of 6 MPa is well below the 500 MPa increase in protoplasmic drought tolerance induced in intact S. stapfianus plants by drought (Ghasempour et al 2001). Nevertheless, several S. stapfianus genes thought to be associated with desiccation tolerance (Neale et al 2000;Le et al 2007) are induced by methyl jasmonate (unpublished result) further supporting a role for methyl jasmonate in desiccation tolerance in S. stapfianus.…”

Changes in phytohormones and oxidative stress markers in buried seeds of Vellozia alata

“…During this period there was a period of desiccation, seed water contents returning to initial values. Although one may speculate that SA increases were induced to withstand desiccation due to the involvement of this compound in desiccation tolerance (Ghasempour et al, 2001;Senaratna et al, 2000), it is very difficult to certainly know this, since SA levels were low in non-buried (desiccated) seeds and ABA -which is also involved in conferring desiccation tolerance (Finkelstein et al, 2008) -did not follow the same trend compared to SA. Another factor leading to a rise in endogenous SA concentrations might be a defensive response against fungal and bacterial pathogens (Martínez et al, 2004;Mur et al, 2000), an aspect that warrants further research.…”

Desiccation-tolerant plants in dry environments

“…Brassinosteroids, methyl jasmonate, and ethylene promoted PDT in S. stapfianus to a higher degree than ABA, but not to a sufficient level to allow the plant to survive desiccation. Of the hormones normally associated with cell differentiation and growth, auxins had no effect, while cytokinins had a deleterious effect on PDT (Ghasempour et al 2001).…”

“…In S. stapfianus, ABA level increases 6-fold during strong drought stress, and reaches a maximum during severe desiccation (20-10% relative water content). However, studies with S. stapfianus protoplasts showed that exogenously applied ABA only promotes protoplasmic drought tolerance (PDT) to a degree that is very much less than is required for desiccation tolerance (Ghasempour et al 2001). Brassinosteroids, methyl jasmonate, and ethylene promoted PDT in S. stapfianus to a higher degree than ABA, but not to a sufficient level to allow the plant to survive desiccation.…”