Diagnosis of Mineral Deficiencies Using Plant Tests

242

142

Sugar beets (Beta vulgaris L. cv F58-554H1) were cultured hydroponically for 2 weeks in growth chambers with two levels of orthophosphate (Pi) supplied in half strength Hoagland solution. Low-P plants were supplied with 1/20th of the Pi supplied to control plants. With low-P treatment, the acid soluble leaf phosphate and total leaf P decreased by about 88%. Low-P treatment had a much greater effect on leaf area than on photosynthesis. Low-P decreased total leaf area by 76%, dry weight per plant by 60%, and the rate of photosynthesis per area at light saturation by 35%. Low-P treatment significantly decreased the total extractable activity of phosphoglycerate kinase (by 18%) and NADPglyceraldehyde-3-phosphate dehydrogenase (by 16%), but did not decrease the total activities of ribulose-1,5-bisphosphate (RuBP) carboxylase (RuBPCase) and ribulose-5-phosphate kinase. Low-P treatment decreased the initial activities of three rate-limiting Calvin cycle enzymes, but had no effect on the initial activity of RuBPCase. Furthermore, low-P treatment significantly increased the total extractable activities of fructose-1,6-bisphosphatase (by 61%), fructose-1,6-bisphosphate aldolase (by 53%), and transketolase (by 46%). The results suggest that low-P treatment affected photosynthetic rate through an effect on RuBP regeneration rather than through RuBPCase activity and that the changes in Calvin cycle enzymes with low-P resulted in an increased flow of carbon to starch.

Section: Resultssupporting

confidence: 93%

Leaf Phosphate Status, Photosynthesis, and Carbon Partitioning in Sugar Beet

Rao

Terry²

1989

242

142

“…For example, it is known that plants increase the activity of their phosphatases in response to P deficiency (see ref. 2 for review). The increases in the level of phosphatases in roots help to release phosphate bound up in root cell walls and perhaps even in the soil (32).…”

Section: Discussionmentioning

confidence: 99%

Leaf Phosphate Status, Photosynthesis, and Carbon Partitioning in Sugar Beet

Al²,

Terry³

1990

124

The effect of low phosphate supply (low P) was determined on the diurnal changes in the rate of carbon export, and on the contents of starch, sucrose, glucose, and fructose 2,6-bisphosphate (F2,6BP) in leaves. Low-P effects on the activities of a number of enzymes involved in starch and sucrose metabolism were also measured. Sugar beets (Beta vulgaris L. cv. F58-554H1) were cultured hydroponically in growth chambers and the low-P treatment induced nutritionally. Low-P treatment decreased carbon export from the leaf much more than it decreased photosynthesis. At growth chamber photon flux density, low P decreased carbon export by 34% in light; in darkness, export rates fell but more so in the control so that the average rate in darkness was higher in low-P leaves. Low P increased starch, sucrose, and glucose contents per leaf area, and decreased F2,6BP. The total extractable activities of enzymes involved in starch and sucrose synthesis were increased markedly by low P, e.g. adenosine 5-diphosphoglucose pyrophosphorylase, cytoplasmic fructose-1,6-bisphosphatase, uridine 5-diphosphoglucose pyrophosphorylase, and sucrose-phosphate synthase. The activities of some enzymes involved in starch and sucrose breakdown were also increased by low P. We propose that plants adapt to low-P environments by increasing the total activities of several phosphatases and by increasing the concentrations of phosphate-free carbon compounds at the expense of sugar phosphates, thereby conserving Pi. The partitioning of carbon among the various carbon pools in low-P adapted leaves appears to be determined in part by the relative capacities of the enzymes for starch and sucrose metabolism.

“…The adequate zone may be specified by the low and high concentrations that cause growth reductions of 5 to 10% from maximum. This is analogous to plant mineral nutrition for which yield is plotted against metal concentration in tissue and the adequate zone lies between the concentrations for critical deficiency and critical toxicity (Bouma, 1983). Adequate zones are windows of concentration (e.g.…”

Section: Metal Tolerancementioning

confidence: 99%

Phytochelatins and Related Peptides (Structure, Biosynthesis, and Function)

Rauser¹

1995

647

271

Plants obtain micronutrients such as Cu and Zn from aquatic and terrestrial environments that may also provide the metals Cd, Pb, and Hg. These essential and nonessentia1 metals exist at low to high concentrations depending on natural and manmade disturbances. In a fluctuating environment the plants may experience shifting internal concentrations of these bioreactive metals. Therefore, it is beneficial for plants to have mechanisms that (a) maintain internal concentrations of essential metals between deficient and toxic limits and (b) keep nonessential metals below their toxicity thresholds. The proteins and peptides known as MTs sequester metals and thereby may accomplish cellular metal homeostasis and detoxification. These molecules are rich in Cys's that provide thiols for binding the metals mentioned so far.The early work on plants was modeled after equine renal MT, a metal-induced protein with 20 Cys's distributed uniquely within the sequence of 60 amino acids and M, of approximately 9000 (Robinson et al., 1993). Studies of yeasts, algae, and plants relied heavily on isolating the metal-induced components of M , of approximately 9000 that bound Cd or Cu. In many of these preparations Cys, Glu, and Gly accounted for 45 to 97% of the amino acids, which is inconsistent with a dose relationship to the archetypal form, equine renal MT. Two independent groups, one working with the fission yeast Schizosaccharomyces pombe (Kondo et al., 1984) and the other working with cultured cells of Rauvolfia serpentina (Grill et al., 1985), showed that the molecules binding Cd were a family of peptides with the primary structure (y-Glu-Cys),-Gly, where n = 2 to 7