Različiti aspekti inhibicije rastenja i fotosinteze kukuruza (Zea mays L.) uzrokovanog herbicidom sulfosatom, 3 - uticaj uzrasta biljaka

Abstract

U radu je razmatran uticaj herbicida sulfosata na rastenje, akumulaciju i preraspodelu suve mase, kao i fotosintezu biljaka kukuruza različitog uzrasta (5, 6 i 7 nedelja). Zapaženo je da akumulacija suve mase (In DW), koja u krajnjem određuje rastenje, kod biljaka kukuruza uzrasta 5 i 7 nedelja visoko značajno koreliše sa zapreminom korena (Vr) i udeonom suvom masom stabla (SMR), dok kod biljaka uzrasta 6 nedelja visoko značajno koreliše sa udeonom suvom masom korena i listova (RMR, LMR). Pored toga biljke uzrasta 6 nedelja imaju statistički značajno veći sadržaj hlorofila a (Chla), u najmlađem potpuno razvijenom listu, u odnosu na biljke uzrasta 5 i 7 nedelja. Na osnovu iznetog možemo pretpostaviti da postoje razlike između biljaka ovih uzrasta i u pogledu reakcije fotosintetskog aparata na stres herbicidom sulfosatom. Tako je, po svemu sudeći, regulacija fotosinteze kod biljaka kukuruza uzrasta 5 i 7 nedelja u uslovima stresa herbicidom sulfosatom nezavisna od fotosistema 2 (PS II), što je u skladu sa literaturnim podacima o dejstvu ovog herbicida. Nasuprot tome, regulacija fotosinteze biljaka kukuruza uzrasta 6 nedelja u uslovima stresa herbicidom sulfosatom regulisana je tzv. nefotohemijskim gašenjem fluorescencije Chla (pokazatelj NPQ). To je optimalan način regulacije fotosinteze u uslovima stresa i predstavlja aklimacioni odgovor. Uzimajući u obzir i faktore koji određuju akumulaciju suve mase biljaka uzrasta 6 nedelja, ne možemo isključiti pretpostavku da je fotosinteza kod biljaka kukuruza ovog uzrasta regulisana promenama u tzv. "proizvođač-potrošač" odnosima.

Effects of the herbicide sulphosate on the growth, accumulation and allocation of dry weight and photosynthesis in maize plants of different age (5, 6 and 7 weeks) were investigated. Dry weight accumulation (In DW), which ultimately determines growth, was found to correlate highly significantly with root volume (Vr) and stem mass ratio (SMR) in maize plants aged 5 and 7 weeks, while in plants aged 6 weeks a highly significant correlation was found with root mass ratio (RMR) and leaf mass ratio (LMR). Besides, plants aged 6 weeks had a significantly higher content of chlorophyll a (Chla) in the youngest fully developed leaves, compared to plants aged 5 and 7 weeks. Based on these findings, we assumed there was also a difference between plants in these age groups in terms of the reaction of their photosynthetic systems to stress caused by the herbicide sulphosate. Regulation of photosynthesis in the sulphosate-stressed maize plants aged 5 and 7 weeks is thus most probably independent of photosystem 2 (PS II), which is consistent with literature data on the activity of that herbicide. On the other hand, photosynthesis in the sulphosate-stressed maize plants aged 6 weeks is regulated by non-photochemical quenching of Chla fluorescence (whose indicator is NPQ). It is an optimal way through acclimation for regulating photosynthesis under stress. Taking also into consideration the factors that determine dry weight accumulation in maize plants aged 6 weeks, we should not disregard the possibility that photosynthesis in maize plants of that age group may be regulated by changes in the "source-sink" ratios.