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 preparation of, and studies on, free cell suspensions from mouse pancreatic islets