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Abstract Recent studies on chilling tolerance mechanisms in maize revealed a significant positive correlation between genotypic chilling tolerance and chilling-induced accumulation of the stress hormone abscisic acid (ABA) under controlled growth chamber conditions. Based on this and other results, the hypothesis was developed that chilling tolerance in maize is related to the ability to accumulate large amounts of ABA rapidly, as a protection against chilling injury. The objective of the present study was to test this hypothesis under field conditions during natural cold weather periods in spring, which often cause severe chilling injury in maize fields. In two experiments at two locations in Europe with contrasting climates, eight maize genotypes with different genotypic chilling tolerance were cultivated in spring in the field according to agronomic practice for maize. Before and at the end of cold weather periods, ABA levels and water contents were determined in the third leaves. It was found that chilling-tolerant genotypes accumulated higher amounts of ABA during the chilling period than chilling-sensitive genotypes. A significant positive correlation between chilling tolerance and the levels of ABA in the leaves was found. These results support the above-mentioned hypothesis. In contrast to earlier studies performed under growth chamber conditions, the water content in chilled leaves was mostly higher than in non-chilled leaves. The increase in ABA is therefore not attributable to chilling-induced water deficit, but probably to the low temperature itself. [ABSTRACT FROM AUTHOR]

We studied chilling-induced changes of 1-aminocyclopropane-1-carboxylic acid (ACC) and of 1-(malonylamino)- cyclopropane-1-carboxylic acid (MACC) contents in seedlings of ten maize genotypes with different chilling tolerance. Seedlings at the third leaf stage were chilled at 5 °C and at 65 % RH. Immediately before and after two and five days of chilling the contents of ACC and of MACC in the third leaf were measured. Water content and — after recovery — the degree of necrotic injuries and the percentage of seedling survival were also determined. After 2 days of chilling, the ACC content increased in all genotypes investigated. The increase was significantly higher in the sensitive genotypes than in the tolerant ones. There was a significant correlation between ACC content and necrotic injuries of seedlings. Chilling for 5 days increased the ACC content further and the difference between the two groups of genotypes still existed. The MACC content increased after 5 days of chilling in all genotypes investigated. The increase was greater in the tolerant genotypes than in the sensitive ones. However, the difference in MACC accumulation between the two groups of genotypes investigated was not significant, and thus no correlation between MACC accumulation and chilling susceptibility was found. The possible causes for the increase of ACC and MACC contents under chilling conditions and the possibility of using the ACC content as an indicator of chilling tolerance in maize breeding are discussed. [ABSTRACT FROM AUTHOR]

The protective effect of a synthetic terpenoid analog of abscisic acid (ABA), coded LAB 173711, on transplant shock in rice was investigated under field conditions. Rice seedlings (Fujisaka 5 and IR 20) were taken from a seed bed and their roots were immersed in aqueous solutions of the growth regulators for 24 h. Afterwards they were drought-stressed for 3 or 6 h by exposing them to direct sunlight before they were transplanted to the field. A pretreatment with either LAB 173711 alone or in combination with the growth retardant tetcyclacis reduced the loss of water during the exposure to sunlight, increased the percentage of survival of the seedlings in the field, and increased the percentage of grain filling of the plants which had survived. The combined application of growth regulators was most effective and may be useful for minimizing transplant shock in rice and other crops. [ABSTRACT FROM AUTHOR]

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