CHANGES IN IONS AND PROTEINS IN PITH OF INTERNODES OF A SHRUNKEN2 SWEET MAIZE AT 4 DEVELOPMENTAL STAGES

Physiological processes change as plants age. This study was conducted to determine how concentration of ions, and distribution of proteins, change in senescing stalk internodes of a sweet maize (Zea mays L.). 'Illini Gold', a shrunken2 hybrid, was monitored from mid-whorl (V9; i nternodes completely juvenile) to fresh-market maturity (FM; internode s exhibiting stages of senescence). Internodes near the base of the st alk, just below the ear, and between an ear and tassel were rated for senescence. These same tissues were extracted and analyzed by SDS-PAGE electrophoresis and automated ion analysis. Senescence rating in inte rnodes increased from V9 or VT to FM. Concentrations of NO3-, Na+, tot al Fe, and total Mn were unchanged, while those of total N, in a Kjeld ahl digest (TKN), and K+ were reduced in all internodes as plants aged . In one or more internodes, concentrations of total P, in a Kjeldahl digest (TKP), HPO42-, Mg2+, Ca2+, and SO42- either were unchanged, flu ctuated, or decreased as plant aged. Concentrations of TKN, TKP, HPO42 -, Mg2+, and SO42- were negatively correlated with senescence rating i n one or more internodes. The least number of protein bands, between 1 4.4 and 97.4 kD, were found on gels at FM. Changes in concentration of some ions, and distribution of proteins may indicate the onset of sen escence.