Cellular Processes Limiting Leaf Growth in Plants under Hypoxic Root Stress

The effects of root hypoxia on leaf growth of a Populus trichocarpa? deltoides hybrid have been assessed. Clonal plants were subjectedto hypoxic root conditions in pot culture by flooding and insolution culture by gassing with nitrogen. The rate of leafexpansion declined within 8 h and was suppressed for the durationof the treatment. Final leaf size was reduced by 35% to 60%compared to aerated plants. Final epidermal cell size and numberdepended both on the developmental stage of the leaf at theonset of stress and on the duration of the treatment. No differencesin bulk leaf water potential were measured between the hypoxicand aerated plants. Cell wall extensibility was lower, leafsolute potential was more negative and turgor potential washigher in leaves of hypoxia-treated plants than of aerated plants.These data suggest that leaf growth of hypoxia-stressed plantsis limited by cell wall extensibility. The mechanism by whichthe root stress induces changes in leaf cell wall characteristicsis not known. Key words: Populus, flooding