Issue link: http://read.dmtmag.com/i/197178
SOILCOHEN & CELLAR REMI Understanding Plant Hormones Applied growth regulators can impact vine, berry physiology lant hormones are chemicals that regulate growth and are often referred to as plant growth regulators (PGR). These molecules are signal molecules that regulate processes such as bud break, shoot elongation, formation of plant parts such as leaves, clusters, and tendrils, flower and berry development and ripening, root growth, and abscission of leaves and roots. Plant hormones are often produced during the differentiation of cells at active meristem locations, such as the sites of production of new roots, shoot elongation or cluster differentiation. Exogenous (external) applications of PGRs have been used, although more often in table grapes than in wine grapes, to promote dormancy, increase berry size and enhance ripening. Understanding both plant response to exogenous hormone applications and endogenous hormones helps elucidate the complex relationships among hormones in regulating vine physiological development. THE ABCS OF ABA PGRs regulate bud break, shoot elongation and many other aspects of plant development. Photo: Thinkstock The concentration of hormones required for plant response can be as low as 10−6 to 10−5 mol/L (moles per liter), making them difficult to research. It has only been since the late 1970s that scientists have made significant advances in studying their effects and relationships to plant development. There are many classes and types of hormones found in grape vines, and their complex interactions regulate critical processes such as shoot growth and cessation, grape ripening, seed and vine dormancy, and vine response to stress. w w w. v w m m e d i a.com Abscisic acid (ABA) is generally considered to be an inhibitory chemical compound that affects many processes in vine and berry physiology. ABA is produced mostly in the chloroplasts of leaves, but also in roots during periods of water stress. ABA is critical in regulating bud growth and bud and seed dormancy. ABA mediates changes in apical meristems, and it initiates bud dormancy and stimulates the alteration of the last set of leaves into bud covers. The presence of ABA also prevents bud growth, which is important during winter dormancy. The slow dissipation of ABA in buds prevents them from growing during warm spells in winter, providing some protection until the AT A GLANCE + Plant hormones regulate critical processes such as shoot growth, grape ripening and vine response to stress. + Plant hormones and their effects are complex and interrelated. + Abscisic acid initiates and maintains seed and bud dormancy, impacts cessation of shoot growth, leaf senescence and veraison, and regulates vine response to water stress. + Auxins, cytokinins and N ov - D ec 2013 giberellins are hormones involved in early berry development, from set through lag phase. | V INE YA RD & W INE RY M A N A G EM EN T 33