Jure KOLARIČ
pp. 31-36

Abscission is a morphogenetic process, which is genetically regulated and plays several rules in plant life. Abscission of young apple (Malus domestica Borkh.) fruits is especially important to prevent alternate bearing and to improve several quality parameters of mature fruits. For stimulation of fruitlets abscission different chemical substances can be used. Chemical substances act by prevention of pollination/fertilization (bloom thinning) or by stimulation of fruitlets drop (fruit thinning). Although the chemical thinning is well known technological measure in fruit growing, the mode of action of different chemical thinners is still unclear. Researchers believed that chemicals can act by interfering hormonal state in plant, inhibiting assimilate production, or affect on polar auxin transport (PAT). However, until now none of these theses have been fully confirmed. Since abscission is genetically controlled process, several experiments were designed to indentify genes related to abscission in the last years. Until now groups of genes related to ethylene biosynthesis, to auxin efflux/influx carriers, to carbohydrate metabolism and to hydrolytic enzymes were identified. All mentioned genes are differently down- or up regulated during the abscission process and to clarify the role of these genes in abscission more experiments have to be designed.

Key word: apples, abscission, fruit thinning, ethylene, AZ

REFERENCES

1. Arteca NR. Plant growth substances. Chapman&Hall, New York, 1995:45-222.

2. Bangerth F. Abscission and thinning of young fruit and their regulation by plant hormones and bioregulators. Plant Growth Regul. 2000;31:43-59.

3. Beruter J, Droz P. Studies on locating the signal for fruit abscission in the apple tree. Sci. Hortic. 1991;46:201-14.

4. Bonghi C, Tonutti P, Ramina A. Biochemical and molecular aspects of fruitlet abscission. Plant Growth Regul. 2000;31:35-42.

5. Byers ER. Flower and fruit thinning and vegetative fruit balance. In: Ferrere DC in Warington IJ. Apples. Cabi publishing, Cambridge, 2003:437-58.

6. Črnko J. Redčenje zlatega delišesa s Sevinom, Amid-Thinom w in NAA. Jug. voć. 1981;15,55-56:305-10.

7. Črnko J, Marn M. Chemical fruit thinning in apple cultivars `Jonagold` and `Idared`. Jug. voć. 1985;19,73-4:365-9.

8. Dal Cin V, Boschetti A, Dorigoni A, Ramina A. Benzylaminopurine application on two different apple cultivars (Malus domestica) displays new and unexpected fruitlet abscission features. Ann. Bot. London. 2007;99: 1195-202.

9. Dal Cin V, Rizzini FM, Botton A, Tonutti P. The ethylene biosynthetic and signal transduction pathways are differently affected by 1-MCP in apple and peach fruit. Postharvest Biol. Tec. 2006;42:125-33.

10. Dal Cin V, Barbaro E, Danesin M, Murayama H, Velasco R, Ramina A. Fruitlet abscission: A cDNA-AFLP approach to study genes differentially expressed during shedding of immature fruits reveals the involvement of a putative auxin hydrogen symporter in apple (Malus domestica L. Borkh). Gene 2009a;442:26-36.

11. Dal Cin V, Velasco R, Ramina A. Dominance induction of fruitlet shedding in Malus domestica (L. Borkh): molecular changes associated with polar auxin transport. Bmc. Plant. Biol. 2009b;9:139.

12. Dennis FG. The history of fruit thinning. Plant Growth Regul. 2000; 31: 1-16.

13. Dennis FG. Mechanisms of action of apple thinning chemicals. HortScience, 2002; 37(3):471-474.

14. Ebert A, Bangerth F. Relations between the concentration of diffusible and extractable gibberellins-like substances and the alternate bearing behavior in apple as affected by chemical fruit thinning. Sci. Hortic. Amsterdam, 1981;15:45-52.

15. Ebert A, Bangerth F. Possible hormonal modes of action of three apple thinning agents. Sci. Hortic. Amsterdam. 1982;16:343-56.

16. Faust M. Physiology of temperate zone fruit trees. John Wiley and sons, New York, 1989:338.

17. Greene DW, Autio WR, Erf JA, Mao ZY. Mode of action of benzyladenine when used as a chemical thinner on apples. J. Am. Soc. Hortic. Sci. 1992;117(5):775-9.

18. Greene DW. Chemicals, timing, and environmental factors involved in thinner efficiacy on apple. HortScience, 2002;37(3):477-81.

19. Harada T, Sunako T, Wakasa Y, Soejima J, Satoh T, Niizeki M. An allele of the 1-aminocyclopropane-1-carboxylate synthase gene (Md-ACS1) accounts for the low level of ethylene production in climacteric fruits of some apple cultivars. Theor. Appl. Genet. 2000;101:742-6.

20. Kim J, Shiu SH, Thoma S, Li WH, Patterson SA. Patterns of expansion and expression divergence in the plant polygalacturonase gene family. Genome Biol. 2006;7(9): R87.

21. Lay-Yee M, Knighton ML. a full-length cDNA encoding 1-aminocyclopropane-1-carboxylate synthase from apple. Plant Physiol. 1995;107(3):1017-8.

22. Li CJ, Bangerth F. Autoinhibition of indolacetic acid transport in the shoots of two-branched pea (Pisum saetivum L.) plants and its relationship to correlative dominance. Physiol. Plantarum 1999;106(4):415-20.

23. Pandita VK, Jindal KK. Enzymatic and anatomical changes in abscission zone cells of apple fruits induced by ethephon. Biol. Plantarum 1991;33(1):20-5.

24. Roberts JA, Elliot KA, Gonzalez-Carranza ZH. Abscission, dehiscence and other cell separation processes. Annu. Rev. Plant. Biol. 2002;53:131-58.

25. Rosenfield CL, Kiss E, Hrazdina G. MdACS-2 (accession no. U73815) and MdACS-3 (accession no. U73816): two new 1-aminocyclopropane-1-carboxylate synthases in ripening apple fruit. Plant Physiol. 1996;112(4):1735.

26. Ruperti B, Bonghi C, Tonutti P, Ramina A. Ethylene biosynthesis in peach fruitlet abscission. Plant Cell Environ. 1998;21:731-37.

27. Sexton R. Abscission. In: Pessarakli. Handbook of Plant and Crop Physiology, New York, 1995:497-525.

28. Stopar M, Black BL, Bukovac MJ. The effect of NAA and BA on carbon dioxide assimilation by shoot leaves of spur-type `Delicious` and `Empire` apple trees. J. Am. Soc. Hortic. Sci. 1997;122:837-40.

29. Sunako T, Ishikawa R, Senda M, Akada S, Niizeki M, Harada T. Plant Gene Register PGR 00-030. MdACS-5A (accession no. AB034992) and 5B (accession no. AB034993), two wound-responsive genes encoding 1-aminocyclopropane-1-carboxylate synthase in apple. Plant Physiol. 2000;122(3):620.

30. Unrath CR. Spray volume, canopy density, and other factors involved in thinner efficiency. Hort. Sci. 2002; 37(3):481-3.

31. Wertheim SJ. Developements in the chemical thinning of apple and pear. Plant Growth Regul. 2000; 31: 85-100.

32. Westwood MN. Temperate-Zone pomology. Timber press, Portland, 1992:523.

33. Wiersma P, Zhang H, Lu C, Quail A, Tovonen PMA. Survey of the expression of genes for ethylene synthesis and perception during maturation and ripening of `Sunrise` and `Golden Delicious` apple fruit. Postharvest Biol. Tec. 2006;44:204-11.

34. Yuan R. Effects of temperature on fruit thinning with ethephon in `Golden Delicious` apples. Sci. Hortic. 2007;113:8-12.

35. Zhou C, Lakso AN, Robinson TL, Gan S. Isolation and characterization of genes associated with shade-induced apple abscission. Mol. Genet. Genomics 2008;280:83-92.