Differential ethylene-inducible expression of cellulase in pepper plants

Ethylene promotes the abscission of leaves and the ripening of fruits in pepper plants, and in both events an increase in cellulase activity is observed. However, two enzyme isoforms (pI 7.2 and 8.5, respectively) are differentially involved in the two physiological phenomena. The pI 8.5 form has been purified from ripe fruits. It is a glycoprotein with an apparent molecular mass of 54 kDa. Two short peptides were sequenced and a very high homology to a tomato cellulase was observed. Polyclonal antibodies, raised against the purified enzyme, have allowed us to demonstrate that the observed ethylene-induced increase in cellulase activity is paralleled by de novo synthesis of protein. Three cDNAs (CX1, CX2 and CX3), encoding different cellulases, were obtained and characterized and their expression investigated. Accumulation of all three mRNAs is induced by ethylene treatment, though to different levels. CX1 is mainly expressed in ripe fruits while CX2 is especially found in abscission zones. CX3 accumulates at very low levels in activated abscission zones. Comparisons with other known cellulases demonstrate clear heterogeneity within the higher plant cellulases. Differences in ethylene inducibility and molecular structure suggest different physiological roles for cellulase in pepper plants.This paper is dedicated to Prof. G. Dall'Olio on the occasion of his 70th birthday.     

Ultrastructural study of an olive necrotic mutant of maize

Summary Ultrastructural surveys, carried out into an olive necrotic maize mutant (Neuffer E 283 B) grown under a 16 hours photoperiod, have shown remarkable morphological alterations in the plastids. Such alterations, affecting both the mesophyll and the bundle sheath plastids, appear to be photodependent. Quite normal etioplasts are present in dark-grown mutant seedlings. Moreover, light appears also to inhibit the overall growth of mutant plants. 12-day-old mutant plants grown under illumination are 4 cm in comparison with the 10 cm of the wild type, while corresponding dark-grown seedlings of both types are 12 cm high.Supported by a grant of C.N.R.     

Tapetum plastids ofOlea europaea L.

Summary The plastid ontogenesis inOlea europaea tapetum has been studied. Tapetum plastids start their development as proplastids and differentiate into elaioplasts. At the end of their development the tapetal cells degenerate and are substituted by roundish lipidic masses which will later form an exine coating (Pollenkitt). During their ontogenesis the plastids are characteristically associated with membrane outlines of mostly smooth ER, which appear to be correlated with lipid accumulation inside the plastids.