Pigment development on immature c-p ears

Chen and Coe reported (1977) that c-p seeds required both light and germination conditions to develop anthocyanin pigment. They also reported that immature c-p seeds did not develop pigment during maturation if exposed to light, but that the seed could "store" the light signal and use it later to develop anthocyanin when germinated in the dark. However, immature c-p seeds do not strictly require germination conditions to form pigment when removed from the ear. Strong anthocyanin pigment formed with seeds 30 days after pollination, removed from the ear and allowed to dry for 48 hours under light. Thus some condition present when the seeds are on the ear apparently prevents the light signal from being utilized by the c-p seeds.

In the 1978 greenhouse, several c-p (W22) self-pollinated ears were exposed to light, with the purpose of obtaining material which had "stored" a light signal. Surprisingly, these seeds developed pigment while still on the plant, and in distinct morphogenetic patterns. Three major types of events were observed: 1) crown pigmentation--pigment on the crown of the kernel, ranging in intensity from a pale blush of pigment up to fairly dark pigmentation; 2) pigment bands--a band of pigment on the lateral faces of the kernel, at the crown-base interface and 3) pigment clones--pigmented areas that resembled the clonal losses observed when the C-I allele is lost from C-I/C/C aleurone. These events occurred most often on the side of the ear most exposed to the light (i.e., the side opposite stalk insertion) and were more frequent and more darkly pigmented on ears that had been exposed early (18-25 DAP) than on ears that were exposed to light later in development (30-33 DAP). Some seeds showed all three types of events. If both bands and crown pigment were found on the same seed, there was usually a colorless zone between the crown pigment and the banded region. The clones are sometimes quite large with irregular shapes; the smaller clones are very similar in appearance to the C-I loss clones, being rectangular or square in outline. Clonal areas superimposed on pale crown pigment sometimes appeared to be twin spots composed of a colorless and more darkly pigmented region.

The areas of pigment that developed on the c-p(W22) ears in the greenhouse 1978 season were not observed until after 30 DAP, whereas C(W22) seeds are fully pigmented by 18 DAP. Thus if the physiological conditions are altered in certain regions of the seed so that these areas are no longer restricted (in whatever manner) from using the light signal, then the crown pigmentation and the banded pigment patterns can perhaps be explained. It is more difficult to explain the clonal regions of pigment, especially since some of these clones appeared to be twin spots. Twin spots are usually explained by somatic crossing-over or non-disjunction of chromosomal segments; thus the occurrence of these clonal regions may be related to the genetic organization of the C locus. For example, if the C locus is composed of a series of genetic units and a certain number of these units are required for c-p-like expression and a larger number of these units are required for C-like expression, then somatic crossing-over could yield sectors that have acquired enough units to develop pigment on the ear when given a light signal. It is also possible that the sectors are due to somatic loss of an inhibitor component at the c-p allele. For example, if the c-p allelic structure is with the (I) component preventing utilization of the light signal while the seed is still on the ear, then c-p(-)/c-p(I)/c-p(I) seeds might be able to develop pigment on the ear, due to the reduced dosage of the hypothetical (I) element.

Sheila McCormick

Please Note: Notes submitted to the Maize Genetics Cooperation Newsletter may be cited only with consent of the authors.

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