RESUMEN
Land plants lose vast quantities of water to the atmosphere during photosynthetic gas exchange. In angiosperms, a complex network of veins irrigates the leaf, and it is widely held that the density and placement of these veins determines maximum leaf hydraulic capacity and thus maximum photosynthetic rate. This theory is largely based on interspecific comparisons and has never been tested using vein mutants to examine the specific impact of leaf vein morphology on plant water relations. Here we characterize mutants at the Crispoid (Crd) locus in pea (Pisum sativum), which have altered auxin homeostasis and activity in developing leaves, as well as reduced leaf vein density and aberrant placement of free-ending veinlets. This altered vein phenotype in crd mutant plants results in a significant reduction in leaf hydraulic conductance and leaf gas exchange. We find Crispoid to be a member of the YUCCA family of auxin biosynthetic genes. Our results link auxin biosynthesis with maximum photosynthetic rate through leaf venation and substantiate the theory that an increase in the density of leaf veins coupled with their efficient placement can drive increases in leaf photosynthetic capacity.
Asunto(s)
Ácidos Indolacéticos/metabolismo , Fotosíntesis , Pisum sativum/fisiología , Proteínas de Plantas/metabolismo , Homeostasis , Mutación , Oxigenasas/genética , Oxigenasas/metabolismo , Pisum sativum/anatomía & histología , Pisum sativum/genética , Fenotipo , Filogenia , Hojas de la Planta/anatomía & histología , Hojas de la Planta/genética , Hojas de la Planta/fisiología , Proteínas de Plantas/genética , Estomas de Plantas/anatomía & histología , Estomas de Plantas/genética , Estomas de Plantas/fisiología , Transpiración de Plantas , Agua/fisiologíaRESUMEN
In recent years the biosynthesis of auxin has been clarified with the aid of mutations in auxin biosynthesis genes. However, we know little about the effects of these mutations on the seed-filling stage of seed development. Here we investigate a key auxin biosynthesis mutation of the garden pea, which results in auxin deficiency in developing seeds. We exploit the large seed size of this model species, which facilitates the measurement of compounds in individual seeds. The mutation results in small seeds with reduced starch content and a wrinkled phenotype at the dry stage. The phenotypic effects of the mutation were fully reversed by introduction of the wild-type gene as a transgene, and partially reversed by auxin application. The results indicate that auxin is required for normal seed size and starch accumulation in pea, an important grain legume crop.
Asunto(s)
Ácidos Indolacéticos/farmacología , Pisum sativum/metabolismo , Semillas/anatomía & histología , Almidón/biosíntesis , Ácido 2,4-Diclorofenoxiacético/farmacología , Regulación de la Expresión Génica de las Plantas/efectos de los fármacos , Genes de Plantas , Germinación/efectos de los fármacos , Germinación/genética , Mutación/genética , Tamaño de los Órganos/efectos de los fármacos , Pisum sativum/efectos de los fármacos , Pisum sativum/embriología , Pisum sativum/ultraestructura , Fenotipo , Plantas Modificadas Genéticamente , Plantones/efectos de los fármacos , Plantones/genética , Plantones/crecimiento & desarrollo , Semillas/efectos de los fármacos , Semillas/ultraestructura , Sacarosa/metabolismo , Factores de Tiempo , Cigoto/efectos de los fármacos , Cigoto/metabolismoRESUMEN
The recently discovered group of plant hormones, the strigolactones, have been implicated in regulating photomorphogenesis. We examined this extensively in our strigolactone synthesis and response mutants and could find no evidence to support a major role for strigolactone signaling in classic seedling photomorphogenesis (e.g. elongation and leaf expansion) in pea (Pisum sativum), consistent with two recent independent reports in Arabidopsis. However, we did find a novel effect of strigolactones on adventitious rooting in darkness. Strigolactone-deficient mutants, Psccd8 and Psccd7, produced significantly fewer adventitious roots than comparable wild-type seedlings when grown in the dark, but not when grown in the light. This observation in dark-grown plants did not appear to be due to indirect effects of other factors (e.g. humidity) as the constitutively de-etiolated mutant, lip1, also displayed reduced rooting in the dark. This role for strigolactones did not involve the MAX2 F-Box strigolactone response pathway as Psmax2 f-box mutants did not show a reduction in adventitious rooting in the dark compared with wild-type plants. The auxin-deficient mutant bushy also reduced adventitious rooting in the dark, as did decapitation of wild-type plants. Rooting was restored by the application of indole-3-acetic acid (IAA) to decapitated plants, suggesting a role for auxin in the rooting response. However, auxin measurements showed no accumulation of IAA in the epicotyls of wild-type plants compared with the strigolactone synthesis mutant Psccd8, suggesting that changes in the gross auxin level in the epicotyl are not mediating this response to strigolactone deficiency.