Different Response To Boron Deficiency And Their Mechanism In Cotton Cultivars With Different Boron Efficiency

The different response to boron deficiency and their mechanism in cotton cultivars with different boron efficiency was studied under soil and solution culture condition. Main results are as follows: 1. There are obvious differences in growth and development between cotton cultivars with different boron efficiency under boron deficiency. The differences reaches the top when the boron concentration is from 0.003 mg/L to 0.005 mg/L in nutrient solution, this boron concentration is critical level for research on boron efficiency differences in cotton cultivars. 2. The growth and development of roots in two cotton cultivars were decreased by boron deficiency, which resulted in that the amount of root bleeding sap and the amount of nutrients in bleeding sap cut down, the reduce degree in boron efficient cotton cultivar were obviously less than boron inefficient one. The results suggested that absorption capacity to water and nutrients were more in boron efficient cultivar than in boron inefficient one, it is an important reason why there are the different boron efficiency in two cotton cultivars. 3. The content and accumulation of boron in different parts of B-inefficient cotton cultivar were greater than those in B-efficient cotton one under sufficient boron supply, which suggested the B-inefficient cotton cultivar require more boron for normal growth. The reduce of boron content and boron accumulation in different parts and total boron accumulation in the whole plant of B-inefficient cotton cultivar were more than those of B-efficient cotton one by boron deficiency. The boron distribution rate in cotton leaves were decreased under insufficient boron supply, but the trendy was more obvious in young leaves of B-inefficient cotton cultivar, this suggested more boron were translocated into young leaves probably from the boron absorbed by roots from environment or from the boron stored in other organs in B-efficient cultivar. 4. The accumulation of Ca and Mg in two cotton cultivars was depressed by boron deficiency, but amount of decrease in B-inefficient cotton cultivar was more. The distribution rate of Ca and Mg in the bottom leaves was no obvious change in both cotton cultivar when boron supply was insufficient, but those was increased in the upper leaves of B-efficient cotton cultivar and decreased in B-inefficient cotton one. These results indicated that B-efficient cultivar had greater absorption capacity to Ca and Mg than B-inefficient one under boron deficiency, maybe also have greater capacity of translocation or retranslocation to the nutrients. 5. The biomass of calyx, corolla, stamen, pistil and the whole floral organ were not significantly affected in B-efficient cotton cultivar by B deficiency, however, decreased in B-inefficient one. The content of soluble sugar, starch, free proline and soluble protein in corolla, stamen and pistil and pollen viability were markedly cut down in both cotton cultivars by boron deficiency, but the amount of reduce in B-inefficient cotton cultivar was more than B-efficient cotton one. 6. Boron concentration and accumulation in all parts of cotton floral organs such as bracteal leaf, calyx, corolla, stamen, and pistil were obviously decreased by boron deficiency. Generally, there was a downward trend in the concentration and accumulation of Cu, Zn, Mn and Fe in all parts of cotton floral organ under B deficiency, but their reduce degree was less than those of B. When boron was deficiency, the accumulation of B, Cu, Zn, Mn, Fe, N, P, K, Ca and Mg were more in stamen and pistil of B-efficient cotton cultivar and less in bracteal leaf than that of B-inefficient one, but the differences of those nutrients accumulation in calyx and corolla between both cultivars were very little. Those were probably because of the different efficiency of uptake, transportation, distribution or redistribution between two cultivars. 7. Almost no boron was determined in cotton phloem exudation sap whether boron supply was sufficient or insufficient, it suggests B mobility in cotton was restricted. Boron concentration and exudation rate in xylem sap of two cotton cultivars were decreased by boron deficiency, but the trendy was more obviously in B-inefficient cultivar. The B concentration in xylem sap of both cotton cultivars was lower than that in nutrient solution under sufficient boron supply (0.5 mg/L), but the contrary trendy was found at a B supply of 0.002 mg/L, B concentration in xylem sap was up to 32 fold in the efficient cultivar and 20.5 fold in the inefficient one higher than in the nutrient solution. Those indicated that there may be two different mechanisms for B translocation into xylem, a passive diffusion process play an important role at sufficient B supply, but a concentration mechanism was turned on in low B condition. It seems the latter mechanism is easy to be turned on in efficient cotton cultivar. 8. The content of pectin and different boron fraction in the B-inefficient cotton cultivar was much greater than in B-efficient one at the supply of B sufficiency. It indicated that B requirement in plants might be predicted by pectin content, which provided a possible tool to determine differential B efficiency among genotypes. The content of water soluble boron and acid soluble but water insoluble boron was depressed in both cotton cultivars under severe B deficiency. The difference of the ratio of water soluble boron content in young leaves to old leaves was greater than that of the content of water soluble boron or insoluble boron between both cotton cultivars with different B efficiency, it might be a better index to mirror the difference of B efficiency among genotypes. 9. When two cotton cultivars were suffered from boron deficiency, malonyl dialdehyde(MDA) content and membrane permeability in their leaves were increased, the activity of protective enzymes such as superoxide dismutase(SOD), peroxidase(POD) and catalase(CAT), the double bond index and the ratio of unsaturated to saturated fatty acid were decreased, however, the increase or decrease degree of boron efficient cultivar was less than that of inefficient one. 10. When spraying polyamines on the leaves of both cotton cultivars at a sufficient or insufficient boron supply, the activity of protective enzymes such as SOD and CAT was increased, and the membrane permeability was decreased in their leaves and roots, however, the change degree was more obvious in B-inefficient cultivar under B deficiency. The putrescine (Put) content was significantly reduced by boron deficiency in both cultivars, but with greater intensity in boron inefficient one. Boron deficiency caused a marked increase of the content of spermidine(Spd), spermine(Spm) and Spd+Spm+Put in boron efficient cultivar, but only an upward trend in the inefficient cultivar. Those suggested that greater polyamines content in boron efficient cultivar under boron deficiency condition resulted in greater activity of protective enzymes, which might remain membrane function integrity.