Occurrence of Sugar Alcohols Determines Boron Toxicity Symptoms of Ornamental Species

Abstract

ADDITIONAL INDEX WORDS. polyols, boron mobility, dieback, diagnosis, tissue sampling ABSTRACT. The phloem mobility of boron (B) in plants varies dramatically among species. Variations in phloem B mobility occur as a consequence of the presence of sugar alcohols (polyols) in some species but not in others, and these differences in phloem B mobility profoundly affect the expression of B toxicity symptoms. Twenty-four species including common ornamental species varying in sugar alcohol content, were selected to test their response to B toxicity. Species that do not produce sugar alcohols exhibited previously described B toxicity symptoms that include accumulation of high concentrations of B in, and burning of, the tip and margin of old leaves. In the sugar-alcohol-producing species these symptoms were absent, and B toxicity was expressed as meristematic dieback and an accumulation of B in apical tissues. These symptoms have not previously been associated with B toxicity in these species and hence may have been frequently misdiagnosed.

Combined effect of salinity and excess boron on plant growth and yield

“…A small number of plants have been found to have mobility of B in phloem as well. In those plants, toxicity is exhibited as meristematic dieback and in apical tissues (Brown et al 1999). In the present study, most of the crops investigated (pepper, wheat, and tomato) are understood to be "Bimmobile".…”

Micronutrient Deficiencies in Global Crop Production

“…Non-polyol producing plants show burning of the tip and margin of old leaves under B toxicity, while in the polyol-producing species these symptoms are absent and toxicity is expressed as meristematic dieback (Fig. 11.1 and in Colour Plates) (Brown et al, 1999). The differences in expression are a consequence of the site of B accumulation that occurs in the oldest tissues of phloemimmobile species and in the youngest tissues of species in which B is phloem-mobile.…”

“…Stunting is a characteristic of Zn deficiency in children. Thus, unless an individual has been monitored for height and weight over several months, there is no quick and easy diagnosis as there is for Fe deficiency, but a survey by Brown et al (1999) of Zn in global diets resulted in a map of putative Zn deficiency (dietary Zn deficiency), and these authors came up with an estimate of 2.6-3 billion people at risk. A map from this seminal work ( Fig.…”

“…The first major advance was the demonstration that B is unique among the plant nutrients in that species differ dramatically in their capacity for phloem B transport and their sensitivity to B deficiency (Brown and Shelp, 1997;Brown et al, 1999). In the majority of plants, B has restricted phloem mobility, while in species that produce polyols (sorbitol, mannitol, and dulcitol, etc.…”

“…Boron toxicity in phloem immobile species is expressed as marginal leaf scorch on the oldest leaves (1a), in species exhibiting phloem B mobility toxicity is expressed as death of youngest growing tips, necrosis of vascular cambium and deformation of fruits. For a full list of species in each symptom category see Brown et al (1999) Boron (B) acetic acid extractable, 231 B concentration in irrigation water, 166, 167 defi ciency, 1,3,8,9,11,28,41,44,45,[96][97][98][99]131,132,139,153,154,159,166,167,181,226,231,262,270,271 defi cient soils,26,96 effi cient genotypes,26,262,264 fertilisers,9,10,33,35,36,41,44,45,54,55,59,72,118,227,254,267,268,278,279,…”