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ABSTRACrPlants of Xanthium strumarium L. and Lycopersicon escuentum Mill. cv 'Rheinlands Ruhm' were grown in solution culture, and control and steam-irdled intact plants were stressed. Detached roots of both species were stressed to different extents in two ways: (a) either in warm air or, (b) in the osmoticum Aquacide III. The roots of both species produced and accumulated progressively more abscisic acid (ABA), the greater the stress inflicted by either method. ABA-glucose ester levels in Xanthium roots were not affected by water stress and were too low to be the source of the stress-induced ABA. The fact that ABA accumulated in detached roots and in roots of girdled plants proves that ABA was synthesized in the roots and not merely transported from the shoots.Maximum ABA accumulation in detached roots occurred after 60 to 70% loss of fresh weight. In Xanthium roots, ABA levels continued to increase for at least 11 hours, and no catabolism was apparent when stressed roots were immersed in water, although the roots did stop accumulating ABA. When osmotically stressed, Xanthium roots reached a maximum ABA level after 2 hours, but ABA continued to rise in the medium.Under optimal stress conditions, endogenous ABA levels increased 100 times over their prestress values in detached roots of Xanthium, and 15 times in Lycopersicon under nonoptimal stress, when endogenous ABA was expressed as concentrations based on tissue water content. These are much greater relative increases than observed in the leaves (15 times in Xanthium, 3 times in Lycopersicon), although the roots contain substantially less ABA than the leaves in all circumstances. The results suggest that the endogenous level of ABA in roots could rise appreciably prior to leaf wilt, and could modify the plant's water economy before the leaves become stressed.There have been many investigations into stress-induced ABA accumulation in leaves, both on the intact plant (2, 3) and when excised (14,23). It is now well established that endogenous ABA levels in leaves increase considerably when plants are water stressed (6,22).On the other hand, the response of roots to water stress is much less clearly understood (1). There (12,20,21), although the results appear to vary from species to species. Osmotically stressed young maize roots also increased their endogenous ABA levels, and ABA was released into the surrounding medium (19).In this paper, we present data on the effect of water stress inflicted by different methods on endogenous ABA levels in cocklebur and tomato roots. MATERAIAS AND METHODSCulture of Plant Material. Xanthium strumarium L., Chicago strain, was grown in solution culture in two different ways. First, seedlings were suspended from perforated boards over trays containing a shallow layer of half-strength Hoagland nutrient solution without aeration. The plants were grown in a greenhouse under the conditions described previously (24) until sufficient roots had developed for experimentation. Second, seedlings were taken from the culture trays after...

Roots of flc and sit-recovered the ability to accumulate stress-induced ABA when grafted with RR scions before the stress was imposed.The ABA-deficient wilty mutants of Lycopersicon esculentum Mill., flc3 and sit, are characterized by a strong tendency to wilt, together with epinastic leaves, reduced leaf area, and aerial root formation (19). The mutant fic, isolated by Stubbe (17), has a lower endogenous ABA level than the wild type, and has been investigated in various studies (1,10,13,14,20,21 The role of ABA in the regulation of phenotype, including morphology and wilting behavior, may be clarified by altering the endogenous ABA levels in the mutants by grafting. Additional information on the effect of the mutated genes on ABA metabolism in turgid and stressed plants may be obtained from reciprocal grafts. Thus, in this paper, we present data on the effects of reciprocal grafts on the phenotype of wild-type and mutant scions and on the accumulation of ABA in response to water stress by roots and leaflets of single genotypes and reciprocal grafts.

ABSTRAC[Isolated guard cells, prepared by sonication of epidermal peels, were used to investigate the endogenous level of abscisic acid (ABA) in the guard cells of turgid and stressed leaves of Vicia faba L. and the argenteum (arg) mutant of Pisum sativum L. The guard cells of V. faba and arg were found to contain 18 and 8 times more ABA, respectively, when isolated from stressed leaves than from turgid leaves. Isolated guard cells of V. faba were also directly stressed with the osmoticum Aquacide III. These guard cells were capable of producing stress-induced ABA to at least 3 times their ABA level when non-stressed.ABA is thought to be involved in the regulation of stomatal behavior during water stress as application of ABA to intact leaves or epidermal strips induces stomatal closure (7,8,23), and wilted leaves accumulate large amounts of endogenous ABA (8,23,27). Even the rapid stomatal closure observed during the onset of stress, before bulk leaf ABA levels rise in response to the stress (2, 15), appears to be induced by a redistribution of the mesophyll ABA (4, 14). However, there have been no direct measurements so far of the endogenous ABA content of guard cells.In this paper, isolated guard cells, prepared by the sonication of epidermal peels (10, 21), were used to investigate directly the endogenous ABA levels in the guard cells of turgid and stressed leaves.Guard cells prepared by sonication appear to be fully functional in many respects; for example in stomatal opening (21), photochemical activity (11), response to ABA (22), K+ uptake (26), malate formation in the light (21), and catabolism of ABA (12). The guard cells should be relatively little affected by their isolation from other leaf cells, at least in the short term, since the mature guard cells do not have plasmodesmata (25,29).Guard cell preparations from two species were compared. The argenteum mutant of Pisum sativum (20) was used as it has a high stomatal density and the epidermis is only loosely attached to the underlying mesophyll (16,18). Viciafaba was investigated as sonicated strips of this species have previously been used in a number of studies (11,12,21,22,26 daily. Recently expanded leaves of both species were used throughout the experiments. The stomatal density of both epidermises of arg and of the lower epidermis of V. faba was determined using a haemocytometer. The dry weight per unit area of sonicated strips from both species was also determined.Guard Cell Preparation. The epidermis was peeled from both adaxial and abaxial leafsurfaces of arg, and with as little adhering mesophyll as possible. The upper and lower epidermises were stored separately in 0.1% Tween 20 in deionized H20 at O°C. The strips were then sonicated with a Branson Sonic Power Sonicator (Branson Instrument Inc., Danbury, CT), equipped with 1.27 cm horn, to remove any adhering mesophyll cells and to break and remove the contents from the epidermal cells. The strips were sonicated up to 5 times in fresh ice-cold aqueous Tween 20. Each sonication period did...

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To meet the increasing demand for natural rubber (NR), currently sourced from the tropical rubber tree Hevea brasiliensis, and address price volatility and steadily increasing labor costs, alternate rubber-producing species are in commercial development. One of these, guayule (Parthenium argentatum), has emerged on the market as a commercial source of high quality rubber. Non-rubber constituents play an important role in the physical properties of NR products. The intrinsic composition of the two NR materials differs and these differences may be a principal cause of the performance differences between them. We have compared the effect of non-rubber constituents, such as protein, lipids, resin and rubber particle membranes. Firstly, a film casting method was developed to obtain rubber films with a uniform thickness. Secondly, the glass transition temperature of different rubbers was determined by dynamic mechanical analysis, and tensile properties were tested for uncompounded materials. Guayule natural rubber (GNR), from which most of the membranes were removed while in latex form (MRGNR) was found to have higher intrinsic strength than GNR or gel-free NR (FNR). An acetone extraction was performed to quantify the resin and free lipids in the rubber samples.

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