Unpredicted, rapid and unintended structural and functional changes occurred during early domestication of Silphium integrifolium, a perennial oilseed.

MAIN CONCLUSION: Selection for increased yield changed structure, physiology and overall resource-use strategy from conservative towards acquisitive leaves. Alternative criteria can be considered, to increase yield with less potentially negative traits. We compared the morphology, anatomy and physiology of wild and semi-domesticated (SD) accessions of Silphium integrifolium (Asteraceae), in multi-year experiments. We hypothesized that several cycles of selection for seed-yield would result in acquisitive leaves, including changes predicted by the leaf economic spectrum. Early-selection indirectly resulted in leaf structural and functional changes. Leaf anatomy changed, increasing mesophyll conductance and the size of xylem vessels and mesophyll cells increased. Leaves of SD plants were larger, heavier, with lower stomatal conductance, lower internal CO2 concentration, and lower resin concentration than those of wild types. Despite increased water use efficiency, SD plants transpired 25% more because their increase in leaf area. Unintended and undesired changes in functional plant traits could quickly become fixed during domestication, shortening the lifespan and increasing resource consumption of the crop as well as having consequences in the provision and regulation of ecosystem services.

Putative regulatory molecules in plants: evaluating melatonin.

Numerous classes of chemicals have been considered as regulators of various aspects of plant growth and development. In evaluating these putative regulatory molecules, plant biologists have encountered a number of challenges, including: the problem of quantifying substances present at trace levels in extremely complex mixtures; difficulty in obtaining and interpreting phenotypic responses to exogenous applications; and, until recently, the inability to selectively alter endogenous levels of these substances. Melatonin (N-acetyl 5-methoxytryptamine), a methoxylated indoleamine, is a potential regulatory molecule found in plants. Although no specific phenotype is currently associated with melatonin or its analogs in higher plants, it has important and unique biological activity in many other taxa, from algae to primates. In these organisms, melatonin functions as a night signal, coordinating responses to diurnal and photoperiodic environmental cues. We assess the process by which melatonin has been evaluated in plants so far and find that many of the methods for melatonin analysis, which have been adopted from animal studies, are inappropriate for use with plant materials. Thus, despite some interesting preliminary reports, research supporting the case for melatonin as a plant regulator is still in its infancy.

Melatonin in plant organs.

The indoleamine melatonin, a well-known animal chemical, has been identified in extracts from several plant species. The function of melatonin in plants is unknown. Two major functions of melatonin in animals are dark signaling and antioxidant protection. Fruit ripening was used as a model physiological process that involves changes in the oxidative status of an organ. Tomato fruits at various stages of ripeness were sampled. Morning glory (Pharbitis nil Choisy, cv. Violet) and tomato (Lycopersicon esculentum Mill., cv. T5 and Castlemart) organs were collected throughout a light/dark cycle to determine whether melatonin levels increased during the night. No consistent evidence was found that melatonin increased significantly in organs of these plants during the night, as it does in many animals. The melatonin content of the fruits generally increased during ripening up to the mature ripe stage and thereafter as the fruit became over ripe.