Formação de aerênquima e fisiologia de dois genótipos de milho sob diferentes concentrações de fósforo e disponibilidade hídrica

Abstract

The deficiency of phosphorus in the soil and climatic changes have promoted negative consequences on agricultural crops, creating structural and physiological changes in plants, directly affecting the growth and productivity. These modifications occur in physiological, morphological, anatomical, biochemical and molecular characteristics. There are few studies relating the deficiency of phosphorus and water stress in the formation of aerenchyma, a tissue associated with drought tolerance in natural conditions. Therefore, this study discusses the relationship between these factors in maize plants as plant model in the formation of lysigenous aerenchyma. The objective was to evaluate the physiological and radicular anatomical variations of maize genotypes under different concentrations of phosphorus and water availability, with focus on the development of aerenchyma and its relationship with the tolerance to these factors. The plant material consisted of two maize genotypes contrasting for drought tolerance, DKB 390 (tolerant) e BRS 1010 (sensitive). The plants were submitted to different levels of irrigation by 30 days: field capacity, 75%, 50% e 25% of the field capacity, applying nutritive solution, modified on the phosphorus content of 0.1; 0.4; 0.8 mM., with a completely randomized experimental design in a 3x4 factorial schema. It was analyzed: percentage of intercellular spaces of the cortical aerenchyma, thickness of the epidermis, the thickness of the cortex, thickness of the endoderm, diameter of vessel elements of the metaxylem, percentage of xylem, percentage of phloem in the vascular cylinder, net assimilation rate, relative growth rate, biomass allocation in the root, biomass allocation in the stem, biomass allocation in sheet and the phosphorus concentration in plants. It was observed that the DKB390 maize presents a higher percentage of intercellular spaces of the cortical aerenchyma than BRS1010 maize regardless the water and phosphorus availability. The variables of thickness of the epidermis, thickness of the cortex, thickness of the endodermis and diameter of the metaxylem in both genotypes showed significant differences in the two factors. However, the growth variables only presented significant differences under different water availability. Different water availability does not stimulate the formation of aerenchyma in the maize genotypes in pilifera area, but phosphorus deficiency induce the aerenchyma formation only in DKB390 genotype, which demonstrated greater changes in root anatomy, which may provide a better tolerance to water stress, through water irrigation efficiency.