JOURNAL OF ULTRASTRUCTURE AND MOLECULAR STRUCTURE RESEARCH 102, 249-254 (1989) Influence of Exogenous Sucrose on the Greening of Oat’ GABRIELLA PASQUA,* FRANCESCA D&LA VECCHU,P NICOLETTA RASCIO,~ AND GIORGIO CASADORO~ *Dipartimento di Biologia Vegetnle, lJniversitc2 “La Sapienza”, Roma, and fDipartimento di Biologia, Universiti di Paduva, Padova, Italy ReceivedJune 21, 1989, and in revised form August 2, 1989 The greening of roots and leaves has been studied in whole oat seedlings grown on White’s medium either with or without 2% sucrose. The added nutrient promotes chlo- rophyll synthesis and chloroplast differentiation in the roots. Yet it manifests a negative effect in the folk tis- sues where it accelerates the decline in chlorophyll as well BS the chloroplast ultrastructural alterations usually associated with senescence. The negative effect of the nutrient in the leaves is probably a consequence of the addition of exogenous sucrose to the endogenous sugars produced by photosynthesis. The foliar tissues would therefore be in the presence of high sucrose concentra- tions, which are known to be harmful for the photosyn- thetic apparatus. SDS-PAGE analysis of thylakoid poiy peptides from root and leaf chloroplasts has revealed or- gan-specific differences in the electrophoretic patterns. 0 1989 Academic Press, Inc. INTRODUCTION It has been shown by many researchers that roots can differentiate photosynthetically active chloro- plasts when grown in the light. However, it seems that the greening must be imposed by long light exposures (Kirk and Tilney-Bassett, 1978). Observed in cross section, the chloroplast differ- entiation does not take place uniformly throughout the root in different species. For instance, in wheat and barley roots the chloroplasts are usually re- stricted to the innermost cortical layers, while in flax they develop all over the cortical parenchyma (Fadeel, 1962). Whatever the case, both the number of chloroplasts and the amount of chlorophyll are much lower than in the leaves (Kirk and Tilney- Bassett, 1978). The fine structure of the root chloroplasts ob- served in some species (Heltne and Bonnett, 1970; Wroblewski, 1973; Oliveira, 1982; Hldyer-Hansen et al., 1989) is quite similar to that of the correspond- l N. Raacio and G. Casadoro dedicate this paper to Professor Mario Oreenigo on the occasion of his 65th birthday. ing leaf chloroplasts. However, despite this similar- ity, in lemon the root thylakoid polypeptide pattern exhibits some peculiarities (H$yer-Hansen et aE., 1989), thus suggesting an expression organ-specific of some polypeptides. Many researches on the root greening were car- ried out with cultured excised roots. In 1934 White demonstrated the importance of exogenous sucrose for growing excised roots of tomato (review in Weston, 1975). This importance was also demon- strated by R&her et al. (1976) while studying the differentiation of roots from cultured leaf explants of Digitalis purpurea L. More recently, Kumar etal. (1983,1984) found out that exogenous sucrose aids the development of a photosynthetic apparatus in cultured explants of carrot roots. However, the amount is critical since excess or high concentrations of sucrose have an in- hibitory effect, as already seen with Dig&&s pur- purea cultured explants (Riicher et aZ., 1976). The optimal amount appears to be 2% sucrose (Kumar et al., 1984; Dodds and Roberts, 1985). In some cases exogenous sucrose was also shown to have a protec- tive effect on plastid senescence (review in De Vec- chi, 1971; Rascio et al., 1988). Research dealing with the effects of exogenous su- crose on the plastid differentiation have usually been performed separately on excised leaves or roots. These experimental models bring in a number of unknown variables which can add to the specific effects of the supplied nutrient. Since roots and leaves exhibit a different tendency to become green, we thought it of some interest to study the effects of exogenous sucrose on the green- ing of both roots and leaves of intact seedlings which represent an experimental system where all the in- teractions sustaining the developmental processes are always maintained. MATERIALS AND METHODS Plunt material. Kernels of Avenu sativa L. cv. Perona were surface-sterilized using sodium hypochlorite, throug%ly rinsed in sterile distilled water, and then germinated on filter paper moist- 249 0889-1606/99 $3.00 Copyright 6 1989 by Academic Prem, Inc. All rights of reproduction in any form reserved.