Endogenous Growth Regulators in Leaves and Tissue Cultures of Pennisetum purpureum Schum.

Abstract

Summary Endogenous levels of major plant growth regulators were measured in leaves and tissue cultures of Napiergrass ( Pennisetum purpureum Schum.) either by high-performance liquid chromatography or radioimmunoassay. The developmentally young, basal region of the tightly furled innermost four young leaves are highly embryogenic (45% of explants produce embryogenic callus) as compared to the more mature middle (28%) and distal (5%) parts of the same leaves. The basal region contained, on a fresh-weight basis, higher levels of both indole-3-acetic acid (IAA; 19 ngg -1 ) and abscisic acid (ABA; 862 ngg -1 ) as compared to middle (11 ngg -1 and 282 ngg -1 , respectively) and distal (13 ngg -1 and 97 ngg -1 , respectively) regions. Segments from fully expanded “mature” leaves did not form any callus and contained lower levels of endogenous IAA (6 ngg -1 fresh weight) and ABA (364 ngg -1 fresh weight) compared to the basal portion of young leaves. Accumulation of high levels of cytokinins (zeatinriboside, dihydrozeatinriboside, 2-isopentenyladenine) was detected in explants after 10d of culture, at the time of visible callus formation. In comparison to the non-embryogenic callus the embryogenic callus consistently contained higher levels of endogenous IAA (5- to 20-fold) and ABA (3- to 4-fold). Levels of cytokinins in non-embryogenic callus were at least two times that in embryogenic callus. These trends were reproducible during regular maintenance for over a year by subculture at two- to three-week intervals. Callus cultures maintained without subculture lost their embryogenic competence after six weeks and contained only low or nondetectable levels of IAA and ABA. The role of endogenous plant growth regulators in determining the morphogenic competence of leaf explants is discussed.