Prevalent Purple Plants Perennially Puzzle Producers
R.L. (Bob) Nielsen
Agronomy Dept., Purdue Univ.
West Lafayette, IN 47907-2054
Email address: rnielsen
ike the swallows that return every year to San Juan Capistrano, it seems that purpling in young corn returns every year somewhere in Indiana. In recent days, I have received several reports of purpling from widely scattered areas of the state. While mildly attractive from an ornamental standpoint, landlords and tenants alike often become concerned when they see their fields take on a purplish hue that is clearly evident from the window of the pickup at 60 mph.
Biochemical Cause of Purpling. Purpling of corn plant tissue results from the formation of reddish-purple anthocyanin pigments that occur in the form of water-soluble cyanidin glucosides or pelargonidin glucosides (Kim, 1998). †A hybridís genetic makeup greatly determines whether corn plants are able to produce anthocyanin.† A hybrid may have none, one, or many genes that can trigger production of anthocyanin.† That is the reason why purpling may appear in only one of two hybrids planted in the same field. Purpling can also appear in the silks, anthers and even coleoptile tips of a corn plant.†
Agronomic Cause of Purpling. Well, you may say, thatís fine but what triggers the production of the anthocyanin pigments in young corn at this time of year? The answer is not clearly understood, but most agree that these pigments develop in young plants in direct response to a number of stresses that limit the plantsí ability to fully utilize the photosynthates produced during the day.
It has been my experience that the most common contributor to the development of purple corn plants is the combination of bright, sunny days and cool nights (40's to 50's F) when corn plants are in the V3 to V6 stages of development (3- to 6-leaf collar stages). This combination translates to a lot of photosynthate produced during the day, but low rates of photosynthate metabolism during the night, that results in high concentrations of sugary photosynthates in the leaves. Since the anthocyanin occurs in the form of a sugar-containing glucoside, the availability of high concentrations of sugar in the leaves (photosynthesis during bright, sunny days) encourages the pigment formation. Hybrids with more anthocyanin-producing genes will purple more greatly than those with fewer “purpling” genes. In most cases, the purpling will slowly disappear as temperatures warm and the plants transition into the rapid growth phase (post-V6).
Other stresses that can restrict photosynthate metabolism in young corn plants include several that result in restricted root growth, including herbicide injury, severe phosphorus deficiency, soil compaction caused by tillage or planter traffic, excessively wet soils, excessively dry soils, insect injury, and disease injury. The negative effects of such root stresses on photosynthate metabolism can amplify the intensity of the purpling already triggered by a combination of cool nights and bright, sunny days.
What About Yield Losses? Does the leaf purpling lead to yield losses later on? It is important to recognize that the cause of leaf purpling, not the purpling itself, will determine whether yield loss will occurs.
If the main cause is simply the combination of bright, sunny days and cool nights, then the purpling will disappear as the plants develop further, with no effects on yield. If the major contributor to the purpling is restricted root systems, then the potential effects on yield will depend on whether the root restriction is temporary (e.g., cool temperatures & wet soils) or more prolonged (e.g., soil compaction, herbicide injury). Plants can recover from temporary root restrictions with little to no effect on yield.† If the root stress lingers longer, the purpling may continue for some time and some yield loss may result if the plants become stunted.†
If the primary cause is hybrid response to the combination of cool nights and bright, sunny days, the purpling symptoms will be spatially uniform throughout a field. If other stress factors are also restricting root development and/or function, then the purpling symptoms may be spatially variable throughout the field and correlated to soil type, drainage characteristics, or elevation of the landscape. Spatially variable patterns of purple corn may indicate the potential for lingering, yield-limiting stresses that should be more thoroughly investigated.
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Chalker-Scott, Linda. 1999. Environmental Significance of Anthocyanins in Plant Stress Responses. Photochemistry and Photobiology 70(1): 1Ė9.
Christie, P.J., Alfenito, M.R., and Walbot, V. (1994). lmpact of low- temperature stress on general phenylpropanoid and anthocyanin pathways: Enhancement of transcript abundance and anthocyanin pigmentation in maize seedlings. Planta 194: 541-549.
Dixon, Richard A. and Nancy L. Paiva. 1995. Stress-lnduced Phenylpropanoid Metabolism. The Plant Cell 7:1085-1097. American Society of Plant Physiologists. [On-Line]. Available at http://www.plantcell.org/cgi/reprint/7/7/1085. [URL accessed May 2012].
Kim, Jae Hak. 1998. Maize Anthocyanin Pathway. Pennsylvania State Univ. [On-Line]. Available at http://scripts.cac.psu.edu/courses/plphy/plphy597_hef1/mpath.html.† [URL accessed May 2012].† Editorial note: This link is for biochemistry fans!
Nielsen, R.L. (Bob). 2009. Reddish-Purple Corn Plants Late in the Season. Corny News Network, Purdue Univ. [online]. http://www.kingcorn.org/news/timeless/PurpleCorn2.html [URL accessed May 2012].