A number of genes are induced by drought stress, and some of these genes are regulated by the plant hormone abscisic acid (ABA). In tomato (Lycopersicon esculentum), four genes have been identified and isolated that require elevated levels of endogenous ABA for expression: le4, le16, le20, and le25. To gain a better understanding of the role of these genes during stress, their expression has been studied in the drought-resistant relative of tomato, Lycopersicon pennellii. It was determined that homologous genes to all four of the L. esculentum genes were present in the L. pennellii genome. Studies were undertaken to compare the expression characteristics of these genes in L. esculentum, L. pennellii, and their F,. Using two methods of water-deficit imposition, whole plants to which water was withheld and detached leaves that were wilted to 88% of their original fresh weight, it was demonstrated that transcripts of these genes accumulated in L. pennellii in response to water deficit. In general, the increase occurred after a longer period of water deficit in L. pennellii than in tomato. As in droughtsensitive species, ABA levels were elevated by drought stress in L. pennellii, although the levels were reduced compared with those in tomato. AI1 four tomato genes were responsive to ABA in L. esculentum and the F,, but only three of the four genes (/e76,le20, and le2.5) were induced in response to exogenous application of ABA in 1. pennellii. lhe patterns of expression of these genes in L. pennellii are generally similar to that of L. esculentum; therefore, it is suggested that these genes play a similar, yet undefined, role in both genotypes rather than being genes that are responsible for the greater drought resistance of L. pennellii.During drought stress plants experience a number of physiological and metabolic changes, including altered expression of many genes (Skriver and Mundy, 1990;, and a concomitant increase in the concentration of the plant honnone ABA (Zeevaart and Creelman, 1988). The ABA that accumulates during drought stress is required for several of the changes in gene expression that occur during drought stress in tomato (Lycopersicon esculentum) leaves (Bray, 1988). Four tomato genes that are drought induced, le4, le16, le25, and le20, have been characterized

The expression of heat shock proteins (HSPs) was compared between genetically characterized heat tolerant and heat sensitive lines of cotton (Gossypium hirsutum andG. barbadense) using electrophoretic analysis ofin vivo labelled proteins. No differences were observed between the two lines with regard to: the temperature at which HSP synthesis was induced (37°C); the temperature at which HSP synthesis was maximal (45°C); the rates of recovery from HSP synthesis; the duration of HSP synthesis; or the major size classes of HSPs expressed in these two lines. Several HSPs were identified on 2D gels which were expressed uniquely in either the tolerant or sensitive cotton line. However, the HSP pattern displayed in a heat tolerant BC-3 individual was that of the heat sensitive parent.

While it is apparent that the heat shock response is ubiquitous, variabilities in the nature of the heat shock response between closely related species have not been well characterized. The heat shock response of three genotypes of tomato, Lycopersicon esculentum, Lycopersicon pennellii, and the interspecific sexual hybrid was characterized. The two parental genotypes differed in the nature of the heat shock proteins synthesized; the speciesspecific heat shock proteins were identified following in vivo labeling of leaf tissue with [35S]methionine and cysteine. The duration of, and recovery from, heat shock varied between the two species: L. esculentum tissue recovered more rapidly and protein synthesis persisted longer during a heat shock than in the wild species, L. pennellii. Both species induced heat shock protein synthesis at 350C and synthesis was maximal at 37°C.The response of the Fl to heat shock was intermediate to the parental responses for duration of, and recovery from, heat shock. In other aspects, the response of the Fl to heat shock was not intermediate to the parental responses: the Fl induced only half of the L. esculentum specific heat shock proteins, and all of the L. pennellii specific heat shock proteins. A discussion of the inheritance of the regulation of the heat shock response is presented.The response of many organisms to elevated temperature has been characterized and described as the heat shock response (13). While it is apparent that the heat shock response is ubiquitous, variations in the nature of the heat shock response between closely related species have not been well characterized. The heat shock response in plants has been well characterized primarily in two crop plants, soybean (2,8,12) and corn (3, 4), and to a lesser extent in a few other systems (5,7,10,16,17,23). There have been reports on the heat shock response of a cell culture of a wild species of tomato, Lycopersicon peruvianum (19,20,27) sity, including tolerances to abiotic stresses (25). We have been investigating the cell genetics of tomato species, in particular of two species, Lycopersicon esculentum, the cultivated tomato, and Lycopersicon pennellii, a green-fruited, drought-tolerant, and water-use efficient species (18, 25). Sexual and somatic hybridization can produce interspecific hybrids between these two species (22,24). We investigated the heat shock response in these two sexually compatible species to determine the range of variation of expression in the heat shock response and the nature of the expression of the response in the hybrid genotype. The parameters of the heat shock response that were measured included: the mol wt and isoelectric point of the HSPs2 synthesized, the temperatures of induction and of maximal synthesis, the differences in duration of and recovery from the heat shock. All of these parameters were characterized in the interspecific Fl and compared with the parental responses. MATERIALS AND METHODS Plant Materials and Growth Conditions