Effect of Petiole Phloem Disruption on Starch and Mineral Distribution in Senescing Soybean Leaves

Abstract

Normally, starch (sugars) and minerals are redistributed from the leaves to the pods during monocarpic senescence in maturing soybean plants. Petiole phloem destruction (steam girdling), which blocked this redistribution by interrupting export through the petiole, altered the foliar senescence pattern producing a distinctive interveinal yellowing with green areas along the veins on pod-bearing plants. This suggests that blockage of the petiole phloem may cause nutrients to accumulate in the green zones along the leaf veins instead of being redistributed to the pods. In the leaves of untreated plants, starch showed the same distribution pattern as chlorophyll; however, starch was preserved in yellow areas as well as the green zones of the steam-girdled leaves. Mineral analyses ofthe veinal and interveinal zones oftreated leaves and controls showed that the veinal green zones and interveinal yellowing in treated plants were not respectively enriched and depleted in minerals corresponding to a redistribution of minerals within the leaves. Depodding also blocked leafyellowing, net mineral redistribution and starch breakdown. Thus, the pods are able to induce chlorophyll breakdown without net mineral redistribution or starch loss in leaves with petiole phloem destruction. This shows that chlorophyll breakdown is not obligatorily coupled with mineral redistribution or starch breakdown.

Nutrient extraction and exportation by common bean cultivars under different fertilization levels: II - micronutrients

“…Moreover, the low quantity transported through the phloem is responsible for the low concentration of this nutrient in fruits, seeds and storage organs (Dechen & Nachtigall, 2006). Once Mn is incorporated or immobilized in the leaves it cannot be remobilized, not even under induced senescence (Wood et al, 1986). …”

Tansley Review No. 111

“…Inhibition of sucrose phloem transport as a result of pathogen infection of sieve tubes (Osswald & Elstner, 1986) ; Mg or K deficiency (Cakmak, 1994 ;Cakmak et al, 1994) ; petiole phloem destruction (Wood et al, 1986) ; or high apoplastic invertase activity (Von Schaewen et al, 1990) is associated with a rapid development of leaf chlorosis, particularly under high light intensity (Dickinson et al, 1991 ;Cakmak & Marschner, 1992). Similarly, enhancements in chlorosis and necrosis due to increased light intensity are very typical in Zndeficient source leaves, reflected in a massive accumulation of sucrose and starch (Marschner & Cakmak, 1989) causing a high potential for photooxidative damage of chloroplast constituents (Fig.…”

Regulación fotoperiódica de la senescencia foliar post-floración en soja y en otras especies de importancia agronómica

“…la remoción de las vainas generó la degradación más lenta de las clorofilas, sin embargo, la An disminuyó al mismo ritmo que en plantas con vainas (Mondal et al 1978;Wittenbach , 1983Crafts-Brandner & Egli 1987b). La interrupción del floema entre las hojas y las vainas, aumentó el contenido de N (Nooden & Murray 1982) y almidón (i.e., forma de reserva de fotoasimilados) (Wood et al 1986) en las láminas foliares de soja sin demorar el ritmo de degradación de las clorofilas. Por otro lado, en trigo la remoción parcial o total de la espiga en macollos principales no modificó la duración de área verde (Slafer & Miralles 1992;Slafer & Savin 1994).…”