COMPARATIVE CYTOLOGICAL AND BIOCHEMICAL-ANALYSIS OF PROTEIN STORAGE VACUOLES FROM COTYLEDONS AND RADICLES OF COTTON SEEDS

Protein storage vacuoles (PSVs) from radicles and cotyledons of dry co tton seeds were isolated by differential centrifugation following homo genization in glycerol. Protein complement analysis of isolated PSVs w ith one dimensional SDS-PAGE gels revealed similar major storage prote ins, viz. 53 and 48 kDa, with differences in lower molecular mass prot eins. Radicle PSVs have apparently more 35-kDa and less 22-kDa storage protein than do cotyledon PSVs. The mineral composition of whole radi cles, cotyledons and isolated PSVs from radicles and cotyledons was de termined by atomic absorption spectroscopy and colorimetric elemental analyses. The concentration of calcium (Ca), magnesium (Mg), potassium (K) and phosphate (P) was lower in isolated PSVs from radicles than f rom cotyledons, resulting in a marked difference in the Mg/Ca and (MgCa)/K ratios in PSVs from these two sources. Analysis of radicle and c otyledon tissue from dry seeds for mineral distribution with EDX and s canning electron microscopy revealed major concentrations of Mg, K and P in PSVs. These observations indicate that PSVs in radicles are simi lar in protein and mineral composition to PSVs in cotyledons. PSVs in radicles have the potential function as storage organelles to provide minerals and nutrients for radicle growth during imbibition and germin ation.