Fructokinase and Hexokinase from Pollen Grains of Bell Pepper (Capsicum annuum L.): Possible Role in Pollen Germination under Conditions of High Temperature and CO2 Enrichment

Abstract

The processes of pollen grain development and germination depend on the uptake and metabolism of pollen sugars. In pepper (Capsicum annuum L.), initial sugar metabolism includes sucrose hydrolysis by invertase and subsequent phosphorylation of glucose and fructose by hexose kinases. The main objective of this study was to investigate changes in fructokinase (EC 2.7.1.4) and hexokinase (EC.2.7.1.1) activities in pepper flowers during their development, and to study the possible roles of these enzymes in determining pollen germination capacity under high temperature and under CO(2) enrichment, previously shown to modify sugar concentrations in pepper pollen (Aloni et al., 2001 Physiologia Plantarum 112: 505-512). Fructokinase (FK) activity was predominant in pepper pollen, and increased during pollen maturation. Pollen hexokinase (HK) activity was low and did not change throughout pollen development. High-temperature treatment (day/night, 32/26 degrees C) of pepper plants reduced the percentage of pollen that germinated compared with that under normal temperatures (26/22 degrees C), and concomitantly reduced the activity of FK in mature pollen. High temperature also reduced FK and HK activity in the anther. Under high ambient CO(2) (800 micro l l(-1)) pollen FK activity was enhanced. The results suggest that pollen and anther FK may play a role in the regulation of pollen germination, possibly by providing fructose-6-phosphate for glycolysis, or through conversion to UDP-glucose (UDPG) to support the biosynthesis of cell wall material for pollen tube growth. High temperature stress and CO(2) enrichment may influence pollen germination capacity by affecting these pathways.

Spikelet Proteomic Response to Combined Water Deficit and Heat Stress in Rice (Oryza sativa cv. N22)

“…Similar expression patterns with dehydrin and reactive oxygen species scavenging catalase-1 transcript were noticed earlier in tobacco (Rizhsky et al 2002). Furthermore, fructokinases in the anther or pollen could also influence pollen germination either by supplying fructose-6-phosphate for glycolysis or by connecting UDP glucose to support cell wall material biosynthesis for pollen tube growth (Clement and Audran 1995;Karni and Aloni 2002). Using RNAi-mediated suppression, Xu et al (2008) showed a hexokinase (OsHxK10) to be essentially involved in anther dehiscence and pollen germination.…”

Analysis of Transposon Insertion Mutants Highlights the Diversity of Mechanisms Underlying Male Progamic Development in Arabidopsis

“…Pollen fructokinases may play a role in pollen germinapublished results). Putative proteins encoded at these loci are involved in biological functions as diverse as tion and tube growth by providing fructose-6-phosphate for glycolysis or through conversion to UDP-glucose to cell wall biosynthesis, protein anchoring (this work and Lalanne et al 2004), calcium sensing, signaling, metabsupport the biosynthesis of cell wall material (Karni and Aloni 2002).…”

Plastidial Thioredoxin z Interacts with Two Fructokinase-Like Proteins in a Thiol-Dependent Manner: Evidence for an Essential Role in Chloroplast Development in Arabidopsis and Nicotiana benthamiana

“…Recombinant oxidized E. coli TRX (Promega) served as a positive control. Fructokinase activity was determined using a coupled optic enzymatic assay as detailed by Karni and Aloni (2002). To investigate the influence of reduction state on enzyme activity, the recombinant proteins were incubated in the presence of 50 mM DTT, 4 mM recombinant TRX z, or a combination of 10 mM DTT and 4 mM TRX z for 60 min at room temperature prior to the activity measurement.…”