D\u00fc\u015f\u00fck s\u0131cakl\u0131k stresi iki k\u0131s\u0131mda incelenir.<\/p>\n\n\n\n
\u2022\u00dc\u015f\u00fcme Stresi<\/p>\n\n\n\n
\u2022Donma stresi<\/p>\n\n\n\n
D\u00fc\u015f\u00fck s\u0131cakl\u0131k bitkilerde nekrozis, solma, doku y\u0131k\u0131m\u0131,<\/p>\n\n\n\n
esmerle\u015fme, b\u00fcy\u00fcme azal\u0131\u015f\u0131 ve \u00e7imlenme d\u00fc\u015f\u00fc\u015f\u00fc gibi etkiler<\/p>\n\n\n\n
meydana getirerek, verimde \u00f6nemli azalmalara sebep olur.<\/p>\n\n\n\n
Bitkinin d\u00fc\u015f\u00fck s\u0131cakl\u0131klardan etkilenen en \u00f6nemli k\u0131s\u0131mlar\u0131<\/p>\n\n\n\n
k\u00f6klerdir. D\u00fc\u015f\u00fck s\u0131cakl\u0131klarda k\u00f6k b\u00fcy\u00fcmesinde azalma<\/p>\n\n\n\n
meydana gelir ve bu azalma bitkilerin b\u00fcy\u00fcmesini de etkiler.<\/p>\n\n\n\n
Toprak s\u0131cakl\u0131\u011f\u0131n\u0131n d\u00fc\u015fmesi, suyun vizkozitesini<\/p>\n\n\n\n
art\u0131rmas\u0131ndan dolay\u0131, k\u00f6klerin su al\u0131m\u0131 ve membranlar\u0131n suya<\/p>\n\n\n\n
permeabilitesi azal\u0131r. Bu durumda besin al\u0131m\u0131 oran\u0131 da d\u00fc\u015fer.<\/p>\n\n\n\n
<\/p>\n\n\n\n
SO\u011eUK STRES\u0130 (\u00dc\u015f\u00fcme stresi)<\/u><\/strong><\/p>\n\n\n\n Suyun donma noktas\u0131 \u00fczerindeki dondurucu olmayan s\u0131cakl\u0131klar\u0131n<\/p>\n\n\n\n etkisidir ve bitki \u00f6zsuyunun fiziksel durumunda bir de\u011fi\u015fme<\/p>\n\n\n\n meydana getirmeyen s\u0131cakl\u0131klard\u0131r. Tropik ve subtropik bitkiler 10-<\/p>\n\n\n\n 12 \u030a C\u2019nin alt\u0131ndaki dondurucu olmayan d\u00fc\u015f\u00fck s\u0131cakl\u0131klar\u0131n<\/p>\n\n\n\n etkisinde kald\u0131klar\u0131 zaman fizyolojik a\u00e7\u0131dan \u00f6nemli derecede k\u00f6t\u00fc<\/p>\n\n\n\n davran\u0131\u015f g\u00f6sterirler. Donma etkisine sahip olmayan d\u00fc\u015f\u00fck<\/p>\n\n\n\n s\u0131cakl\u0131\u011f\u0131n yapt\u0131\u011f\u0131 k\u00f6t\u00fc etki \u00fc\u015f\u00fcme olarak adland\u0131r\u0131l\u0131r.<\/p>\n\n\n\n So\u011fuk stresinden etkilenmelerine g\u00f6re bitkiler 3 gruba ayr\u0131l\u0131rlar;<\/p>\n\n\n\n \u2022So\u011fu\u011fa hassas olanlar (12\u00b0C\u2019nin alt\u0131ndaki s\u0131cakl\u0131klardan zarar<\/p>\n\n\n\n g\u00f6r\u00fcrler)<\/p>\n\n\n\n So\u011fu\u011fa toleransl\u0131 fakat dona duyarl\u0131 olanlar (12\u00b0C\u2019nin alt\u0131ndaki<\/p>\n\n\n\n s\u0131cakl\u0131klara uyum sa\u011flayabilir, fakat donma s\u0131cakl\u0131klar\u0131nda<\/p>\n\n\n\n hayatta kalamazlar)<\/p>\n\n\n\n \u2022Donmaya toleransl\u0131 olanlar (donma s\u0131cakl\u0131\u011f\u0131n\u0131n alt\u0131ndaki<\/p>\n\n\n\n s\u0131cakl\u0131klarda hayatta kalabilirler ve bu s\u0131cakl\u0131klara uyum<\/p>\n\n\n\n sa\u011flayabilirler)<\/p>\n\n\n\n \u2022So\u011fuk ve donma streslerinin do\u011fas\u0131 farkl\u0131d\u0131r. So\u011fuk stresi<\/p>\n\n\n\n h\u00fccreler \u00fczerine d\u00fc\u015f\u00fck s\u0131cakl\u0131\u011f\u0131n do\u011frudan etkisidir. Donma ise<\/p>\n\n\n\n dolayl\u0131 olarak rol oynar, h\u00fccreleri buz olu\u015fumu ile zarara u\u011frat\u0131r<\/p>\n\n\n\n (Pearce, 1999; Turan ve Ekmek\u00e7i, 2008).<\/p>\n\n\n\n <\/p>\n\n\n\n \u00dc\u015f\u00fcme zarar\u0131 ile elde edilen g\u00f6zlemler iki grup i\u00e7inde toplanabilir.<\/u><\/strong><\/p>\n\n\n\n \u2022Permeabilitedeki de\u011fi\u015fimler<\/p>\n\n\n\n \u2022Metabolik de\u011fi\u015fimler<\/p>\n\n\n\n \u00dc\u015f\u00fcme zarar\u0131n\u0131n b\u00fct\u00fcn \u00e7e\u015fitlerinde esas permeabilitede<\/p>\n\n\n\n de\u011fi\u015fme olmas\u0131d\u0131r. \u00dc\u015f\u00fcmenin oldu\u011fu;<\/p>\n\n\n\n \u2022Direkt( do\u011frudan) zarar ve so\u011fuk \u015foku, so\u011fu\u011fun ans\u0131z\u0131n olmas\u0131<\/p>\n\n\n\n ile a\u00e7\u0131klanabilir, bu da plazmalemma permeabilitesinde artmaya,<\/p>\n\n\n\n h\u00fccre bile\u015fenlerinin kayb\u0131na ve sonunda h\u00fccrenin \u00f6l\u00fcm\u00fcne<\/p>\n\n\n\n sebep olur.<\/p>\n\n\n\n \u2022\u0130ndirek(dolayl\u0131) zarar:<\/p>\n\n\n\n A: Fotosentezin bozulmas\u0131<\/p>\n\n\n\n B: Solunum bozulmas\u0131<\/p>\n\n\n\n C: Toksik \u00fcr\u00fcn art\u0131\u015flar\u0131: asetaldehit, etanol, keto asitler<\/p>\n\n\n\n D: Protein sentezinin engellenmesi ( ATP ara \u00fcr\u00fcn eksikli\u011fi nedeniyle )<\/p>\n\n\n\n Bitkilerde meydana gelen so\u011fuk zarar\u0131 belirtileri<\/u><\/strong>; s\u0131cakl\u0131\u011fa,<\/p>\n\n\n\n so\u011fu\u011fa maruz kalma s\u00fcresine, bitkiye (genotipe), bitkinin geli\u015fim<\/p>\n\n\n\n evresine, so\u011fukla temas eden dokuya, r\u00fczgara, suya, besinlere<\/p>\n\n\n\n ve \u0131\u015f\u0131k gibi di\u011fer \u00e7evresel ko\u015fullara ba\u011fl\u0131 olarak de\u011fi\u015fir (Saltveit<\/p>\n\n\n\n ve Morris, 1990). Genel olarak bu belirtiler; bitki b\u00fcy\u00fcme h\u0131z\u0131n\u0131n<\/p>\n\n\n\n azalmas\u0131, yaprak geni\u015fli\u011finin azalmas\u0131, h\u00fccresel otolizin ve<\/p>\n\n\n\n ya\u015flanman\u0131n artmas\u0131, programlanm\u0131\u015f h\u00fccre \u00f6l\u00fcmleri, \u0131\u015f\u0131kta<\/p>\n\n\n\n fotooksidasyon sonucu klorofil kayb\u0131 nedeniyle klorozis olu\u015fumu,<\/p>\n\n\n\n h\u00fccre zar yap\u0131lar\u0131n\u0131n bozulmas\u0131 ve bunun sonucunda h\u00fccresel<\/p>\n\n\n\n b\u00fct\u00fcnl\u00fc\u011f\u00fcn bozulmas\u0131, protoplazmik ak\u0131\u015f\u0131n en az d\u00fczeye inmesi<\/p>\n\n\n\n ve nekrozis olarak \u00f6zetlenebilir.<\/p>\n\n\n\n D\u00fc\u015f\u00fck s\u0131cakl\u0131klar kinetik etkiler y\u00fcz\u00fcnden t\u00fcm metabolik<\/p>\n\n\n\n reaksiyonlar\u0131 yava\u015flat\u0131r. Ancak, \u00f6zellikle fotosentez a\u00e7\u0131s\u0131ndan iki<\/p>\n\n\n\n duyarl\u0131 metabolik reaksiyon vard\u0131r; bunlar CO2 fiksasyonu ve stoma<\/p>\n\n\n\n a\u00e7\u0131kl\u0131\u011f\u0131n\u0131 d\u00fczenleyen reaksiyonlard\u0131r. Bu nedenle, stoman\u0131n su<\/p>\n\n\n\n kayb\u0131n\u0131 d\u00fczenleme yetene\u011finin ve CO2 de\u011fi\u015fiminin engellenmesi<\/p>\n\n\n\n yapraklar\u0131n so\u011fu\u011fa maruz kalmalar\u0131n\u0131n iki \u00f6nemli sonucudur. K\u00f6k<\/p>\n\n\n\n zar\u0131ndan su ge\u00e7irgenli\u011finin azalmas\u0131 nedeni ile stoma a\u00e7\u0131kl\u0131\u011f\u0131 d\u00fc\u015f\u00fck<\/p>\n\n\n\n s\u0131cakl\u0131klarda genellikle azal\u0131r.<\/p>\n\n\n\n So\u011fuk gibi bir\u00e7ok \u00e7evresel stres, absorblanan \u0131\u015f\u0131k enerjisi ve<\/p>\n\n\n\n yararlan\u0131lan \u0131\u015f\u0131k enerjisi aras\u0131ndaki dengeyi bozar. Bu durum O2<\/p>\n\n\n\n \u2019nin indirgenmesi yerine singlet O2 yani reaktif oksijen t\u00fcrlerinin<\/p>\n\n\n\n (ROT) olu\u015fmas\u0131na neden olur. ROT\u2019un \u0131\u015f\u0131kta meydana gelmesine<\/p>\n\n\n\n \u201cfotooksidatif stres\u201d denir.<\/p>\n\n\n\n DONMA STRES\u0130<\/u><\/strong><\/p>\n\n\n\n Suyun donma noktas\u0131 alt\u0131ndaki s\u0131cakl\u0131klar\u0131n yapt\u0131\u011f\u0131 olumsuz etkisidir.<\/p>\n\n\n\n Donma hasar\u0131 iki \u00f6nemli mekanizmayla olur. Birincisi buz kristalleri<\/p>\n\n\n\n hassas membranlar ve h\u00fccre organizasyonunu bozarak mekanik<\/p>\n\n\n\n hasarlar yapar. \u0130kincisi buz olu\u015fumu sonucu, dokular\u0131n su i\u00e7eri\u011fi<\/p>\n\n\n\n azal\u0131r ve kurakl\u0131\u011fa neden olur. Bilindi\u011fi gibi h\u00fccreler aras\u0131<\/p>\n\n\n\n bo\u015fluklardaki su y\u00fcksek bir su potansiyeline sahiptir. Oysa<\/p>\n\n\n\n sitoplazma ve vakuollerde daha d\u00fc\u015f\u00fck ve daha negatif bir su<\/p>\n\n\n\n potansiyeline sahiptir. B\u00f6ylece buz kristalleri ba\u015flang\u0131\u00e7ta h\u00fccreler<\/p>\n\n\n\n aras\u0131 bo\u015fluklarda olu\u015fma e\u011filimindendir ve h\u00fccreler aras\u0131 buz<\/p>\n\n\n\n kristalleri b\u00fcy\u00fcd\u00fck\u00e7e devam eden donma, protoplasttan suyun<\/p>\n\n\n\n ayr\u0131lmas\u0131na neden olur. Donmaya dayan\u0131kl\u0131 bitkilerin protoplastlar\u0131,<\/p>\n\n\n\n kristallerin erimesi sonucunda suyu tekrar absorbe etme<\/p>\n\n\n\n durumundad\u0131r. Dayan\u0131kl\u0131 olmayan bitkilerde ise su h\u00fccreler aras\u0131<\/p>\n\n\n\n bo\u015fluklarda kalma e\u011filimindedir. \u00dcstelik dayan\u0131ks\u0131z bitkilerde buz<\/p>\n\n\n\n kristalleri protoplast i\u00e7erisinde olu\u015fur ve bitkiye direkt mekaniz zarar<\/p>\n\n\n\n verirler. Bitkilerde donma iki \u015fekilde olur: h\u00fccre i\u00e7i donma, h\u00fccreler<\/p>\n\n\n\n aras\u0131 donma.<\/p>\n\n\n\n Konu Kaynaklar\u0131:<\/p>\n\n\n\n Turan \u00d6., Ekmek\u00e7i Y. . 2008 . The effects of cold stress on plants and<\/p>\n\n\n\n tolerence mechanisms. Anadolu University Journal of Science and<\/p>\n\n\n\n Technology, 9(2): 177-198.<\/p>\n\n\n\n Pearce, R.S. (1999). Molecular analysis of acclimation to cold. Plant<\/p>\n\n\n\n Growth Regul. 29, 47-76.<\/p>\n\n\n\n Saltveit, M.E. ve Morris, L.L. (1990). Overview of chilling injury in<\/p>\n\n\n\n horticultural 196 Anadolu \u00dcniversitesi Bilim ve Teknoloji Dergisi, 9 (2)<\/p>\n\n\n\n crops. Chilling Injury of Horticultural Crops, Eds: C.Y. Wang, ss. 3-15,<\/p>\n\n\n\n CRC Press, Boca Raton, FL<\/p>\n\n\n\n Maliyetler, yeti\u015ftiricilik, dan\u0131\u015fmanl\u0131k ve pazar hakk\u0131nda di\u011fer t\u00fcm detaylar i\u00e7in bize https:\/\/ejdermeyvesipitaya.com\/iletisim<\/a> ula\u015fabilirsiniz.<\/p>\n\n\n\n Ejder Meyvesi Pitaya<\/p>\n\n\n\n
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