131 ACTA UNIVERSITATIS AGRICULTURAE ET SILVICULTURAE MENDELIANAE BRUNENSIS SBORNÍK MENDELOVY UNIVERZITY V BRNĚ Volume LVIII 15 Number 1, 2010 EFFECT OF WATER STRESS ON SELECTED PHYSIOLOGICAL CHARACTERISTICS OF TOMATOES R. Pokluda, K. Petříková, M. E. Abdelaziz, A. Jezdinský Received: November 20, 2009 Abstract POKLUDA, R., PETŘÍKOVÁ, K., ABDELAZIZ, M. E., JEZDINSKÝ, A.: Effect of water stress on selected physiological characteristics of tomatoes. Acta univ. agric. et silvic. Mendel. Brun., 2010, LVIII, No. 1, pp. 131–138 This work presents the results of a field experiment with tomato cv. Proton grown under water stress conditions and under well irrigated conditions. At the same time, the effects of Pentakeep supporting agent (consisting of aminolevulinic acid) was studied. The following characteristics of plant physio- logy were studied – specific leaf area (SLA), leaf water content (LWC) and leaf proline concentration. The obtained results show a significant decrease in SLA during plant vegetation (from 190 to 165 cm −2 . g −1 ). A decrease was also found under water stress treatment (163 cm −2 . g −1 ), in contrast to the well watered control (184 cm −2 . g). LWC values ranged from 81 to 87 % in both seasons. A signifi- cantly important decrease of LWC was found in the stressed variant. Pentakeep application did not af- fect either SLA or LWC characteristics. The level of proline in tomato leaves varied from 0.6 to 1.5 μmol . g −1 . The highly significant effect of water conditions resulted in the increase of proline content under water stress treatment. Although Pentakeep increased the proline content by 9 %, its effect was not of significant importance. The pro- line content was also influenced by the date of sampling. The results indicate that physiological characteristics, such as SLA, LWC and proline content, are good indicators of water stress in tomato, proline content being a particularly reliable parameter cor- responding to the actual water stress of plants. water stress, tomato, specific leaf area, leaf water content, proline Droughts in connection with high temperatures have become the most common abiotic factors in- fluencing physiological processes in plants, and consequently the yield and its quality. Under water stress, plants naturally try to prevent loss of water by means of various mechanisms, such as pore closing (CHAVES et al., 2003), synthesis of osmoprotectants –sugars, aminoacid proline and other substances (RAMANJULU et al., 2002). It has been found out (CLAUSSEN, 2005) that proline content grows sig- nificantly as early as in 14 hours aſter water stress. When assessing stress in hydroponically grown to- matoes, it was found out that proline content in to- mato leaves under water stress was higher in sum- mer than at the end of the vegetation. The level of proline also depends on light intensity. A negative correlation of proline and leaf water content (LWC) was proved. The relative LWC decrease by 5 % dou- bled the increase of proline content. SHTEREVA et al. (2008) mention the possibility to use a ‘proline’ test as an instrument for finding tomato genotypes tolerant to water stress. Apart from the natural mechanisms reducing the stress, new possible uses of complementary sub- stances leading to greater stress endurance of plants are being searched for. One such substance is ami- nolevulinic acid (ALA) which has a number of posi- tive effects on plant physiology. According to KORMAZ et al. (2009), spraying or dipping pepper seedlings in ALA solution clearly reduced the signs of cold damage. At the same time, an exogenous application of ALA increased the con- tent of the monitored constituents, including pro- line. ALA also increased the relative leaf water con-