COMPARISON OF ANATOMICAL AND HISTOLOGICAL DIFFERENCES BETWEEN ROOTS OF BARLEY GROWN IN AERATED AND IN NON-AERATED CULTURE SOLUTIONS

Cytoplasmic acidosis as a determinant of flooding intolerance in plants

We present evidence that cytoplasmic acidosis is a cause of meristematic death in hypoxic root tips of maize and pea seedlings. Usually, leakage of acid from the vacuole is responsible for cytoplasmic acidosis. Leakage of acid, which occurs earlier during hypoxia in pea root tips than in maize root tips, appears to account for the lower tolerance of peas for hypoxia. Cytoplasmic acidosis is accelerated in maize root tips that are either (i) deficient in alcohol dehydrogenase, so that lactic acid production continues throughout hypoxia, or (ii) exposed to external CO2 during hypoxia, or (iii) perfused slowly so that escape of CO2 produced during ethanolic fermentation is retarded. All three conditions decrease the length of time maize root tips can tolerate hypoxia; more rapid cytoplasmic acidosis is associated with more rapid death under hypoxia. Possible mechanisms by which cytoplasmic acidosis leads to death are suggested; the mechanism does not involve inhibition of glycolysis by low pH.

Adaptation of barley roots to low oxygen supply and its relation to potassium and sodium uptake

The uptake of Na(+) and K(+) by barley seedlings grown on aerated or non-aerated solutions was studied. Plants growing in culture solution took up K(+) with high selectivity whether the solution was aerated or not. Roots of plants grown on aerated CaSO(4) and transferred to a solution of KCl and NaCl had a lower preference for K(+) than roots of plants grown on non-aerated CaSO(4). Both kinds of low-salt roots were much less able to discriminate between K(+) and Na(+) than high-salt roots grown on a culture solution. The different levels of K(+) selectivity are suggested to be related to H(+) release from the tissue.

DIFFERENTIATION AND MATURATION OF PRIMARY TISSUES IN WHITE MUSTARD ROOT TIPS

Roots of white mustard (Sinapis alba) were grown either on moist filter paper or in aerated or non-aerated water culture, and detailed measurements of rates of tissue differentiation and maturation were made from sectioned and fresh material. The variation in these rates is shown for a number of roots of each treatment and a comparison made between treatments. The sequence of differentiation and maturation of tissues in this root is similar to that reported previously for other dicotyledonous roots. Differentiated and matured tissues were found closer to the apex in slower growing roots, the differences being more pronounced in some tissues between the treatments. This is discussed in relation to the nutrition of the root.

CAUSES OF INJURY TO PLANTS RESULTING FROM FLOODING OF THE SOIL

Images