Root cortex death and subsequent initiation and growth of lateral roots from bare steles of chickpeas

Abstract

The anatomical responses of chickpea (Cicer arietinum L.) roots to aging and severe water deficits and their capacity for subsequent initiation and growth of new lateral roots after rewatering are only partially known. This study was conducted to characterize the degeneration of epidermal and cortical cells of chickpea roots and the subsequent initiation and growth of new roots from bare steles, i.e., steles surrounded by an endodermis but lacking other parts of the cortex. Chickpea plants were grown in pots in a greenhouse under standard culture conditions (potting mix and daily watering) or drought treatments. For drought treatments, plants were grown in sand and exposed to repeated 10-d treatments of water deficits and rewatering. In standard culture conditions, older cortices collapsed and deteriorated but not simply as a function of chronological age. After one 10-d drought treatment, the epidermis and outer cortex of primary and some secondary and tertiary roots collapsed and after a subsequent rewatering treatment, the epidermis and cortex deteriorated and sloughed from steles. In both standard and drought conditions, bare steles were able to sustain growing root tips, indicating that the endodermis was effective in preserving stelar functions. In droughted plants, bare steles were able to initiate new lateral roots from the pericycle after rewatering, indicating that cortical tissue other than the endodermis was not necessary for secondary and tertiary chickpea roots to initiate new lateral roots. In a given root system exposed to the drought treatments, although the cortex collapsed on some roots, the cortices of other secondary roots did not collapse or deteriorate under similar severe conditions. The reason for cortical survival is unclear, but the response of these roots was similar to roots that have a suberized hypodermal layer which protects underlying cortical tissues from excessive drying. Key words: chickpea, Cicer arietinum L., drought, lateral roots, rewatering.