Photomodulation of mesocotyl elongation in maize seedlings: Is there a correlative relationship between phytochrome,auxin and cell wall extensibility?

Three h white light irradiation of etiolated maize seedlings ( Zea mays L. cv. Jubilee) inhibited mesocotyl elongation and caused a sharp decrease in cell wall plastic extensibility as measured by the Instron technique. The plastic extensibility following white light irradiation (3 h) was photomodulated by phytochrome. Although the photomodulation of the plastic extensibility was correlated with growth during 20 h, no such correlation was observed at shorter times. The addition of indole-3-acetic acid to light-inhibited intact seedlings, or seedlings from which the coleoptile and inner leaves were excised, resulted in a stimulation of growth. However, none of the IAA concentrations could reverse light inhibition. The possibility of a correlative relationship between phytochrome, auxin and cell wall extensibility is discussed.     

Effects of growth state and amines on cytoplasmic and vocuolar pH, phosphate and polyphosphate levels in Saccharomyces cerevisiae: a P-nuclear magnetic resonance study

The vacuoles of logarithmic and stationary stage cells were compared by ³¹P-NMR with regard to pH, orthophosphate (P_i) content and average size of polyphosphate. The vacuoles of stationary cells had lower pH higher P_i content, and polyphosphates of longer average chain lenght, although total polyphosphate content was about the same as in logarithmic cells. The lower vacuolar pH in stationary cells was the major cause of a larger cytoplasmic-vacuolar pH gradient. Addition of NH₄Cl, (NH₄)₂SO₄, methylamine or amantadine at pH 8 to cells in either stage caused an icnrease in both cytoplasmic and vacuolar pH, with little or no change in the cytoplasmic-vacuolar pH gradient. However, the administration of ammonium salts to the cells at pH 8.0 resulted in rapid hydrolysis of the intravacuolar polyphosphate to tripolyphosphate and P_i, with attendant redistribution of P_i between the vacuolar and cytoplasmic compartments.