A cool seedling environment often results in purple leaves in some field. Isolated corn plants with extensive purple colored leaves and stalks late in the season have some relationship in cause. Purple coloration in plants is the result of anthocyanin pigments. Anthocyanin pigments absorb the green spectrum of natural light, reflecting much of the blue and red portions. Chlorophyll pigments absorb the blue and red wave lengths, reflecting the green.
Anthocyanins are water soluble pigments that tend to accumulate in the vacuoles of the epidermal cells. Reflection of higher energetic light blue and red wavelengths of the light could be reducing the availability of that energy to the chloroplasts in the mesophyll, perhaps offering some protection from overload of sugars in those cells. Absorption of the higher energy wavelengths of sunlight by anthocyanins has been hypothesized as protecting cellular membranes from photo damage.
Anthocyanin synthesis is associated with the accumulation of sugars in leaf tissue. Conditions that favor photosynthesis but inhibit distribution of the sugar from the leaf tissue can trigger synthesis of anthocyanins. Seedlings inhibited by soil conditions reducing root growth and thus movement of sugars to root tissue. Reduced phosphorus available, perhaps because of reduced roots growth, inhibits transport of sugars from the photosynthetic cells. Cooler temperatures may inhibit metabolism involved in sugar transport. Insect or pathogen damage to leaves that block the phloem cells of the leaf vascular cells, can cause accumulation of sugars in leaves. Purple color is common in plants with poor pollination a few weeks after flowering as sugars have no place to be transported.
Corn hybrids vary in anthocyanin synthesis genetics, some with a higher tendency to develop purple colors when experiencing sugar transport stresses. Early season development of purple leaves in most plants of a field probably involves cool temperatures and will be only a temporary condition. Even hybrids not tending to show purple could be undergoing a similar stress but not have the genetics for the anthocyanin response.
It is good to observe occurrence of purple leaves in corn for analysis of possible causes. If temporary and generally distributed in a field, it is probably temperature related. If scattered, then it may lead to treatments reducing the occurrence this season or the next.
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About Corn Journal
The purpose of this blog is to share perspectives of the biology of corn, its seed and diseases in a mix of technical and not so technical terms with all who are interested in this major crop. With more technical references to any of the topics easily available on the web with a search of key words, the blog will rarely cite references but will attempt to be accurate. Comments are welcome but will be screened before publishing. Comments and questions directed to the author by emails are encouraged.