Changes in dry weight, osmotic potential, abscisic acid and free proline contents were measured during cold hardening of nine winter wheat varieties differing in freezing resistance. During the first weeks of cold hardening dry weight and proline levels increased and the osmotic potential decreased parallel to the development of freezing resistance. Dry weight reached a broad maximum between the seventh and tenth week of hardening. ABA levels had a sharp maximum around the seventh week of hardening, when the dry weight increase began to cease. Maximal levels of proline were observed seven to ten weeks after the start of cold hardening. The mean and final dry weights, the mean, maximal and final proline contents, as well as the maximal ABA contents of the nine varieties correlated significantly with freezing resistance measured at the end of the hardening period. The possible use of proline and of ABA as biochemical markers for freezing resistance in winter wheat breeding is discussed.

In previous studies in vitro-selection of proline overaccumulating lines of winter wheat (Triticum sativum L. cv. Jo 3063) with increased frost tolerance was reported. These traits were found to be genetically stable. In the present study the improvement of frost tolerance (winter hardiness) under field conditions is confirmed for F 7 progenies of the mutants. Moreover, the mutants accumulated higher levels of glucose and fructose, soluble protein and abscisic acid (ABA) in addition to proline than the wild type under cold hardening conditions in a growth chamber as well as under cold hardening field conditions. ABA and proline levels peaked when the temperature decreased, whereas carbohydrate levels increased more slowly at decreasing temperature. Soluble protein levels also increased during cold hardening, but in addition showed sharp declines during frost periods. Increased carbohydrate levels of the mutants were associated with lower osmotic potential values. The differences in carbohydrate, protein and ABA levels between the mutants and the wild type are probably due to pleiotropic effects of the mutation.

No abstract

Experiments conducted m a phytotron on three rice varieties of different salinity tolerance revealed an increase in the content of endogenous abscisic acid (ABA) with increasing NaCl salinity in IR20 (semi salt‐tolerant), but in Pokkali (salt‐tolerant) and IR28 (salt‐sensitive) the increase in ABA content was marginal. Under sahnity stress, in general, 5 weekly sprayings of ABA (10‐4 mol L‐1) decreased Na and K concentrations in the shoot to the extent of 29.5 % and 3.3 %, respectively. However, ABA application significantly improved the K/Na ratio as well as the chlorophyll fluorescence decrease ratio (Rfd, indicator for potential photosynthetic activity), the number of green leaves per plant and the shoot dry weight. The response of IR20 and IR28 to ABA application was significantly better than that of Pokkali. Increasing salinity caused marked nutrient imbalances, decreased Rfd values and shoot dry weight. The results are discussed in relation to possible mechanism of salinity tolerance.

No abstract