Aust. J. Plant Physiol., 1995,22, 1027-34 Changes in in vivo Protein Complements in Drying Leaves of the Desiccation-tolerant Grass Sporobolus stapfianus and the Desiccation-sensitive Grass Sporobolus pyramidalis J. ~uan~~, D. F. GaffAC, R. D. GianelloAB, C. K. ~lornstedt~~, A. D. ~eale~ and J. D. ~arnill~ *~e~artment of Ecology and Evolutionary Biology, Monash University, Clayton, Kc. 3168, Australia. B~epartment of Genetics and Developmental Biology, Monash University, Clayton, Kc. 3168, Australia. C~orresponding authol;facsimile: +61 3 99055613. Abstract. Protein synthesis in vivo was studied with two-dimensional SDS-PAGE of extracts of leaves on intact drying plants of Sporobolus stapfianus (a desiccation-tolerant grass) and S. pyramidalis (a desiccation-sensitive species). Protein complements were also studied in dried, detached leaves of S. stapfianus (detached leaves are also desiccation-sensitive).Extensive changes in in vivo proteins were observed in S. stapfianus plants drying intact: 25 novel proteins, 10 proteins augmented, 13 proteins decreased and 7 proteins disappeared. Two main phases could be distinguished in leaves as plants dry. In the first phase (85-51% relative water content (RWC) range), 10 novel proteins appeared and 2 proteins increased in content. In the second phase (37-3.5% RWC), 15 novel proteins appeared and 2 proteins increased in content. Some changes in protein patterns were also observed in desiccation- sensitive leaves, i.e. in (a) S. stapfianus leaves drying detached and in (b) drying S. pyramidalis leaves attached. These changes were fewer than those in desiccation-tolerant leaves, i.e. in ( c ) S. stapfianus leaves drying on intact plants; that is, (a) and (b) differed from each other and from (c), which indicates that there is no common injury-related pattern of protein change. These results are consistent with the view that changes in protein complements accompany the induction of desiccation tolerance in drying plants of S. stapfianus. Introduction Desiccation tolerance is common in lower plants and in mature seeds, but is less common in vegetative tissues of higher plants (Gaff 1977). Most resurrection plants survive water potential below -400 MPa and relative water content (RWC) below 8%, even down to air-dryness. They can recover full metabolic activity and resume growth once they regain full turgor; this may take less than 24 h from the time that leaves and soil are rewetted. In the leaves of the dicotyledon Craterostigma plantagineum Hochst., induction of complete desiccation tolerance during drying is paralleled by changes in gene expression; novel specific mRNAs arising during tolerance induction have been used to identify six genes which appear to be correlated with it (Bartels et al. 1990, 1992; Piatkowski et al. 1990; Michel et al. 1993). In the resurrection grass Sporobolus stapfianus Gandoger, extensive changes in in vitro proteins synthesised from mRNA extracted from leaves during and after induction of full desiccation tolerance, involve both novel proteins and proteins of greater abundance (Gaff et al. 1992). An analysis of these changes in S. stapjianus indicated 12 novel nuclear-encoded proteins, which appeared to be correlated with desiccation tolerance. Sporobolus stapjianus has advantages as a subject for examining the basis of desiccation tolerance. Abscisic acid has little effect on the induction of desiccation tolerance, and consequently interpretation of data is not confounded by the many other effects of this plant hormone (Gaff and Loveys 1992). Also, leaves, which are detached when fully hydrated, remain desiccation sensitive during drying. Comparison then, is possible with leaves on plants drying intact, in which full desiccation tolerance is induced durirlg dehydration. Furthermore, comparisons may also be made with desiccation-sensitive species in the same genus, such as S. pyramidalis Beauv. We investigated proteins synthesised in vivo in these two species, to study (a) the extent to which changes in mRNA during drying are reflected in protein complements, including chloroplast-encoded proteins, (b) the changes at progressive levels of water stress, and (c) the proteins best correlated with the onset of induction of desiccation tolerance in S. stapfianus.