Maize Disease Resistance

Abstract

This review attempts to examine research into chilling stress in maize (Zea mays L.) during the last 30 years, with emphasis on molecular and physiological areas which have been studied most extensively, Chilling tolerance is controlled by multiple genes which role and mode of action have begun to be determined. Although much of the research on the cold stress response at the molecular level is related to Arabidopsis where several cold-regulated (COR) genes were characterized, COR genes in maize have also been identified. Recently, a transcriptional factor DREB1/CBF homolog, ZmDREB1A, has been isolated in maize which specifically interacted with the DRE/CRT cis-acting element. The expression of this gene was significantly induced by cold stress. Overexpression of ZmDREB1A induced overexpression of target stress-inducible genes resulting in plants with higher tolerance to drought and freezing stresses, Chilling is mediated through the gradual activation of relevant genes Clue to the altered methylation Status during cold treatment. Transcription factors, calcium-dependent protein kinases and SNF-1 related kinases were also shown to be involved in the cold-stress signal transduction pathway. Although it is well known that exposure to temperatures of 4 to 6 degrees C leads to increases in the leaf ABA content and to a water deficit in maize shoots, it is not clear if ABA accumulates in response to low temperature directly or in response to cold-induced water stress. Additionally, the photosynthetic apparatus of maize has been shown to be highly Susceptible to low temperature-induced photoinhibition and leaves developed at 15 degrees C or below are characterized by a very poor photosynthetic capacity. The oxidative stress and defence mechanisms are expressed differently in tolerant and Susceptible seedlings exposed to low temperature, but their role in improving chilling tolerance remains unclear. Comparative studies of genotypes indicated a high genetic variability in chilling tolerance of the photosynthetic apparatus in the Zea mays species when the leaves were developed at sub-optimal temperature. Genetic analysis indicated that this variability, which may be related to the ability of the plants to develop functional chloroplasts at low temperature, is controlled by multiple genetic loci. Improvement of the chilling tolerance of the photosynthetic apparatus may contribute substantially to improving the performance of maize in temperate regions.