A description is given of the major modifications induced in the pattern of phoiosynthates accumulation by the delayed senescence behaviour of the maize inbred line Lo876o2. The ma|or effects noted are: (1) high water and chlorophyll contents in leaves at physiological maturity, (2) high sucrose content in the stalk during grain filling, (3) husks and cobs with more water, sucrose and proteins, (4) high protem content in the grain. The high level of sucrose m the stalk at physiological maturity protects the plant from stalk rotting organisms.The delayed senescence phcnotype depends on a major dominant gene, the same genetic factor which favours the accumulation of a high level of sucrose in the stalk.In their review on photosynthesis, carbon partitioning and yield GiFFORDanci EVANS (1981) pointed out an important aspect of the physiology of cultivated plants: Although yields have been substantially increased by plant breeding, improvement of the photosynthetic process per se has been unsuccessful. The modification of other plant attributes affecting photosynthetic potential, such as leaf area index and leaf area duration, instead was lound to be more correlated witb increase in yield (E\ ANS 1975). It is weil known, for instance, that in maize the superiority of modern hybrids compared to those of preceeding breeding eras is due, at least in part, to the longer duration of their vegetative apparatus (GROSBIE 1983, DuviCK 1984. In this respect selection for higher yield as applied by plant breeders has counteracted the natural processes leading to plant and leaf senescence.Senescence is probably elicited by the growth of seeds depending on the nutritive requirements of these reproductive structures (SINCLAIR and DE WIT 1975). THOMAS and STODPARD (1977) discuss the onset of senescence which is revealed with a progressive disappearance of chlorophyll from the leaves leading to the loss of photosynthetic efficiency and to a compensation point similar to that of G3 plant (WiLEiAMsand KENNEDY 1977). • Leaf longevity can be increased if flowering and pollination are prevented (MOLISCH 1938). This, however, hmits grain yield. Genotypes with leaves showing, some degree of delayed senescence have been found in experimental populations or in open pollmated vaneties and have been incorporated into advanced breeding lines. This paper describes the phenotype and the inheritance of the delayed senescence habit of the inbred LoB76o2. U.S. Copvrighi Clearance. C.mcr Code Siau-m.m; 0 1 79-9541/86/9703-0193$02.50/0 194 GENTINETTA, Ci-ppi, LEroRi. PHRK;O, MOTTO and SALAMINI Materials and MethodsThe two inbred lines of maize considered were Lo876o2"'") and B73. Lo876o2 has been developed at the Istituto Speritnentalc per la Cerealicoltura in Bergamo. Italy, (rom an adapted version of the synthetic variety 'Stiff Stalk oT (BERTOI-IM et al. 1983). The inhred line is characterized by a long duration of the photosynthetic apparatus even after the seeds attain physiological maturity. The delayed senescence of leaves of Lo876ti2 is co...

Objective of research was (a) to evaluate the influence of pollination-prevention on various metabolic parameters of the two maize inbreds B73 and B14A and their F1, and (b) to gain information on the inheritance of leaf senescence, in response to pollination-prevention. The results show that the visual pattern of leaf senescence, in response to prevention of ear pollination, contrasts markedly between the two inbred lines. Relative to control plants, prevention of ear pollination, causes a premature senescence in B73 and B73 x B14A plants, while leaves of unpollinated B14A remain green and similar in appearance to pollinated controls. Furthermore, prevention of ear pollination induces a sizable reduction of dry matter accumulation of all above-ground material and changes in various metabolic parameters. An accumulation of sucrose in the leaves of unpollinated B73 and B73 x B14A plants is correlated with the development of premature senescence. Finally, the genetic analysis supports suggestions that a single dominant gene is responsible for the differences observed, in the visual pattern of leaf senescence, in response to prevention of ear pollination.

This paper describes a new dominant mutation of maize, Mc, which interferes in the endosperm with the synthesis of storage proteins. The mutant is characterized by an opaque phenotype; it reduces the deposition of zein and it increases the level of methionine. The mutation is specifically related to storage protein synthesis since soluble and insoluble carbohydrates are present at normal levels. The main interest of this mutant lies in its synergistic interaction with opaque-2 in repressing zein synthesis. In the double mutant o2Mc the accumulation of zein is reduced to less than 10% of that of the normal endosperm. The control on zein synthesis exerted by the double mutant is at the level of production or stability of translatable zein mRNAs. The double mutant o2Mc germinates well offering the opportunity of using it in biochemical and molecular studies related to storage protein synthesis; the reduced endosperm weight of o2Mc negates its practical utilization in breeding maize for quality.

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