Water relations of tropical dry forest flowers: pathways for water entry and the role of extracellular polysaccharides

Abstract

Many trees in tropical dry forests flower during the dry season when evaporative demand is high and soil water levels are low. In this study the factors influencing the water balance of flowers from three species of dry forest trees were examined. Flowers had greater mucilage contents than leaves, high intrinsic and absolute capacitances, long time constants for water exchange and high transfer resistances. Flower water potentials were higher than in leaves and did not fluctuate over the lifespan of the flower. Flower water content also remained constant even though evaporation rates were high, suggesting that water was being supplied from the stem. In two of the species, the water potential gradient between flowers and leaves was opposite to that necessary for water transport from stem to flowers through the xylem, and it was therefore hypothesized that water may enter the flower through the phloem. Calculations showed that nectar production in these flowers could drive a sink of sufficient magnitude to allow water input via the phloem equal to water lost from the flower to the atmosphere.

Vascular Function in Grape Berries across Development and Its Relevance to Apparent Hydraulic Isolation

“…The rapid accumulation of sugars that is initiated in the berry mesocarp around the time of veraison is accompanied by a dramatic shift in the proportion of xylem and phloem transport (Lang and Thorpe, 1989;Greenspan et al, 1994Greenspan et al, , 1996. This same shift, albeit more gradual, occurs in many other fleshy fruits such as tomato (Solanum lycopersicum; Ho et al, 1987), apple (Malus domestica; Lang and Ryan, 1994;Drazeta et al, 2004), and kiwifruit (Actinidia deliciosa; Dichio et al, 2003) as well as in the flowers of tropical trees (Chapotin et al, 2003). The sudden reduction in xylem transport to the fruit is perceived as a mechanism to hydraulically isolate the fruit and buffer them from environmental stresses experienced by the parent plant.…”

Giant Flowers of Southern Magnolia Are Hydrated by the Xylem

“…Like all multicellular plant structures existing in a diffusioninadequate world, flowers from bud to bloom require continuous supplies of carbohydrates, nutrients, and water that are supplied by long-distance transport vascular systems (Trolinder et al, 1993;Chapotin et al, 2003;De la Barrera and Nobel, 2004;Galen, 2005). In particular, flowers can be water-hungry structures (Blanke and Lovatt, 1993;Galen et al, 1993;Galen, 2005), and a flower's hydraulic needs increase during anthesis due to nectar secretion and when the unfurled perianth, stamens, and stigmatic surfaces become exposed to an evaporative atmosphere (Patino and Grace, 2002;De la Barrera and Nobel, 2004;Galen, 2005).…”

“…Nonetheless, the few available studies suggest that flowers, unlike leaves, are hydrated by the phloem (Trolinder et al, 1993;Chapotin et al, 2003;De la Barrera and Nobel, 2004;Galen, 2005). A major line of evidence for this comes from differences in water potential (C) and water content (WC) between flowers and the subtending leaves.…”

Estratégia reprodutiva de Cochlospermum orinocense (Kunth) Steud.: fenologia, biologia floral e sistema de cruzamento em uma espécie pioneira de florestas na Amazônia

“…A senescência precoce das fl ores ocorre após o principal período de visitação dos polinizadores e pode ser um mecanismo para economia de água na seca. Na congenérica C. vitifolium Spreng., pioneira de fl orestas tropicais na América Central que exibe morfologia fl oral e estratégia reprodutiva similares, as fl ores mantêm um alto potencial hídrico e transpiram intensa e continuamente na seca (Chapotin et al 2003).…”

“…Fecundidade limitada principalmente pelos recursos da planta foi também observada na autoincompatível Cochlospermum vitifolium, sendo sua relativamente baixa razão semente/óvulo (0,13) atribuída ao efeito do pólen incompatível (Snow & Roubik 1987, Chapotin et al 2003, que pode limitar a disponibilidade de cruzamentos e intensifi car os efeitos da limitação de pólen (Byers & Meagher 1992, Knight et al 2005. A maior razão semente/óvulo em C. orinocense (0,23) reforça a hipótese de que autocompatibilidade induz maior efi ciência reprodutiva ao eliminar os efeitos deletérios do pólen incompatível.…”