Disassembly of the fruit cell wall by the ripening-associated polygalacturonase and expansin influences tomato cracking

Fruit cracking is an important problem in horticultural crop production.Polygalacturonase(SlPG)and expansin(SlEXP1)proteins cooperatively disassemble the polysaccharide network of tomato fruit cell walls during ripening and thereby,enable softening.A Golden 2-like(GLK2)transcription factor,SlGLK2 regulates unripe fruit chloroplast development and results in elevated soluble solids and carotenoids in ripe fruit.To determine whether SlPG,SlEXP1,or SlGLK2 influence the rate of tomato fruit cracking,the incidence of fruit epidermal cracking was compared between wild-type,Ailsa Craig(WT)and fruit with suppressed SlPG and SlEXP1 expression(pg/exp)or expressing a truncated nonfunctional Slglk2(glk2).Treating plants with exogenous ABA increases xylemic flow into fruit.Our results showed that ABA treatment of tomato plants greatly increased cracking of fruit from WT and glk2 mutant,but not from pg/exp genotypes.The pg/exp fruit were firmer,had higher total soluble solids,denser cell walls and thicker cuticles than fruit of the other genotypes.Fruit from the ABA treated pg/exp fruit had cell walls with less water-soluble and more ionically and covalently-bound pectins than fruit from the other lines,demonstrating that ripening-related disassembly of the fruit cell wall,but not elimination of SlGLK2,influences cracking.Cracking incidence was significantly correlated with cell wall and wax thickness,and the content of cell wall protopectin and cellulose,but not with Ca^(2+)content.

Penetration of foliar-applied Zn and its impact on apple plant nutrition status:in vivo evaluation by synchrotron-based X-ray fluorescence microscopy

The absorption of foliar fertilizer is a complex process and is poorly understood.The ability to visualize and quantify the pathway that elements take following their application to leaf surfaces is critical for understanding the science and for practical applications of foliar fertilizers.By the use of synchrotron-based X-ray fluorescence to analyze the in vivo localization of elements,our study aimed to investigate the penetration of foliar-applied Zn absorbed by apple(Malus domestica Borkh.)leaves with different physiological surface properties,as well as the possible interactions between foliar Zn level and the mineral nutrient status of treated leaves.The results indicate that the absorption of foliar-applied Zn was largely dependent on plant leaf surface characteristics.High-resolution elemental maps revealed that the high binding capacity of the cell wall for Zn contributed to the observed limitation of Zn penetration across epidermal cells.Trichome density and stomatal aperture had opposite effects on Zn fertilizer penetration:a relatively high density of trichomes increased the hydrophobicity of leaves,whereas the presence of stomata facilitated foliar Zn penetration.Low levels of Zn promoted the accumulation of other mineral elements in treated leaves,and the complexation of Zn with phytic acid potentially occurred owing to exposure to high-Zn conditions.The present study provides direct visual evidence for the Zn penetration process across the leaf surface,which is important for the development of strategies for Zn biofortification in crop species.