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Part I Four-week old tomato (Lycopersicon esculentum Mill.) seedlings were exposed to different constant temperatures of 15, 25, 35, or 45 c. To determine the effect of temperature on Abscisic Acid (ABA) young and old leaves were harvested at 0, 6, 12, 24, or 48 hand free, hydrolyzable and total ABA were measured using gas liquid chromatographic methods. Temperature had a significant effect on free , hydrolyzable and total ABA in both young and old leaves. Time had a significant effect as a cubic function on all ABA measurements in old leaves but in young leaves a significant effect was observed only on the hydrolyzable ABA. Interactions between temperature and time were observed in both young and old leaves. Young leaves had significantly higher amounts of free and hydrolyzable ABA than did old leaves . The total ABA levels were not significantly different in young and old leaves . Suboptimal temperatures increased ABA levels in the plants, in a manner similar to that of other kinds of stresses. Part II Five- week old tomato plants (Lycopersicon esculentum Mill.) were exposed to day-night temperatures of 10-5, 15-10, 25 - 15, 35-25, or 45-35 C. The day length was 16 h with a light intensity of approximately 400 ~ E m- 2s-1 . Plant tops were sampled at 12, 24 , 48, 68, or 72 h. Free, hydrolyzable and total absciscis acid (ABA) quantities were measured using standard gas chromatographic techniques. Stressful temperatures significantly increased both free and hydrolyzable ABA levels . The highest ABA levels were observed in plants grown at 10-5 C. Although time significantly affected ABA levels, its role needs more precise definition . Due to the similar involvements of ABA in temperature-induced and other stresses, ABA may be hypothesized to be a common mediator for different stresses. Part III Warm season crops: bean (Phaseolus vulgaris) CV . Burpee Stringless Green Pod; corn (Zea mays) CV. Golden ,Jubilee; Cantaloupe (Cucumis melo) cv. Hales Best; eggplant (Solunum melongena) CV. Ichiban; and okra (Hibiscus esculentus) CV . Dwarf Green and cool season crops: beet (Beta vulgari s) CV. Early wonder; lettuce (Lactuca sativa) •CV. Great Lakes; cabbage (Brassica oleracea) cv. Savoy; radish (Raphanus sativus) CV. Scarlet Globe; and pea (Pisum sativum) cv. Little Marvel were exposed to 10, 25 , or 40 C. After 24 h free and hydrolyzable ABA and DPA were measured in the plant tops using standard gas chromatographic methods. Warm season crops exhibited elevated levels of PABA, HABA and DPA under 10 C, compared to those at 25 or 40 c. Cool season crops showed similar PABA , HABA and DPA contents under all temperatures, except pea which had higher PABA and HABA levels at 40 C and beet which showed lower levels of HABA at 25 C as compared to 10 and 40 C. DPA existed at much higher concentrations than ABA in all plants of the two groups. It is concluded that while 1 0 C is stressful to warm season crops and thus the ABA and DPA increases, it is not so favorable to cool season crops. A temperature of 40 C would be stressful to both groups, but as long as water supply to the plant is not limiting the plants would not actively produce ABA . Higher levels of DPA under stressful conditions would warrant consideration and taking into account the role of metabolism in regulation of total ABA in the plant.

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Water management for the irrigation of containerized production remains a task reserved to a highly qualified personnel. Without proper instruments to determine the actual water needs, nursery crops can face growth losses of 20 to 30%. / Reviewing the different methods that are used in field production, tensiometer have shown the greatest potential of adaptation to potted plants. / Tests on the utilization of tensiometer were realized on two peat-vermiculite substrates, using two types of porous cup (1 bat--standard flow and 1 bar--high flow). The instruments were tested while permanently fixed in the growing medium, and temporarily fixed for three hours in the growing medium. / The results show that the instruments give excellent measurements for normal condition of growth, requiring saturation level between 50 and 100%, and that for both mode of operation. / Preferably, the choice of the instrument should be based on the hydraulic characteristics of the substrate. Little difference has been found using both instrument in the substrate 1, but in substrate 2 however, the high flow porous cups have given better response. The high flow cups have higher porosity and bigger pores that suit better substrate 2, which is made of coarser particles.

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Thesis (doctoral)--Universität, Giessen, 2006. / Includes bibliographical references (p. 206-219).