Calcium and the development of aerenchyma and celulase activity in corn seedlings subjected to hypoxia

Abstract

Aerenchyma formation is known as one of the most important anatomical adaptations of plants submitted to oxygen shortage. This tissue develops by action of degrading enzymes and resulting in cell wall loosening. This work was conducted with the objective of verifying aerenchyma development in corn seedlings cv. Saracura - BRS 4154, submitted to hypoxia. The development of aerenchyma was observed in association to cellulase activity. The seedlings were submitted to the hypoxia treatments 4 days after germination , by immersion in a flooding buffer, in the absence and presence of calcium. After 0, 1, 2, 3 and 4 days under hypoxic conditions the evaluation of aerenchyma formation was made by transversal sections of coleoptiles apex , where the development of damages caused by hypoxia were also observed, and the intermediary region of roots. The material for the cellulase assays was collected after each of the hypoxia periods. The activity of cellulase was measured by the viscosimetric method. Aerenchyma formation in the roots increased immediately after the induction of hypoxia and reached 50% of the total cortex area at the fourth day of hipoxia. This organ presented an average aerenchyma area seven times higher than coleoptiles, where the area of intercellular spaces reached 15% of the cortex; cell injuries were observed on 65% of the total seedlings. Cellulase activity showed an initial decrease due to the forced stress, but subsequently increased along with the aerenchyma development. The presence of calcium apparently inhibited the aerenchyma development without affecting the enzymatic activity.