Tuber Physiology and Properties of Starch from Tubers of Transgenic Potato Plants with Altered Plastidic Adenylate Transporter Activity

Abstract

We showed recently that antisense plants with decreased activity of the plastidic ATP/ADP-transporter protein exhibit drastically reduced levels of starch and a decreased amylose/amylopectin ratio, whereas sense plants with increased activity of the transporter possessed more starch than wild-type plants and an increased amylose/amylopectin ratio. In this paper we investigate the effect of altered plastidic ATP/ADP-transporter protein expression on primary metabolism and granule morphology in more detail. Tuber tissues from antisense and sense plants exhibited substantially increased respiratory activity compared with the wild type. Tubers from antisense plants contained markedly increased levels of free sugars, UDP-Glc, and hexose phosphates, whereas phosphoenolpyruvate, isocitrate, ATP, ADP, AMP, UTP, UDP, and inorganic pyrophosphate levels were slightly decreased. In contrast, tubers from sense plants revealed a slight increase in adenine and uridine nucleotides and in the levels of inorganic pyrophosphate, whereas no significant changes in the levels of soluble sugars and metabolites were observed. Antisense tubers contained 50% reduced levels of ADP-Glc, whereas sense tubers contained up to 2-fold increased levels of this sole precursor for starch biosynthesis. Microscopic examination of starch grain morphology revealed that the size of starch grains from antisense tubers was substantially smaller (50%) compared with the wild type. The large starch grains from sense tubers appeared of a more angular morphology, which differed to the more ellipsoid shape of wild type grains. The results suggest a close interaction between plastidial adenylate transport and starch biosynthesis, indicating that ADP-Glc pyrophosphorylase is ATP-limited in vivo and that changes in ADP-Glc concentration determine starch yield, as well as granule morphology. Possible factors linking starch synthesis and respiration are discussed.

Inhibition of the Plastidic ATP/ADP Transporter Protein Primes Potato Tubers for Augmented Elicitation of Defense Responses and Enhances Their Resistance against Erwinia carotovora

“…For example, AATP1(St) antisense tubers accumulated up to 10 times more Glc, exhibited increased ATP to ADP ratios, and increased respiratory activity. In contrast, sense tuber tissues did not exhibit significantly altered Glc levels or ATP to ADP ratios compared with wild-type tubers (Geigenberger et al, 2001).…”

“…Therefore, it seems possible that the increased ATP to ADP ratio in AATP1(St) antisense tuber tissue (Geigenberger et al, 2001) might induce or facilitate the activation of corresponding protein kinases. In addition, the substrate for the plasma membrane-bound oxidase NADPH is synthesized via the cytosolic oxidative pentose phosphate pathway (Emes and Tobin, 1993).…”

“…To determine whether there are differences in the capacity to produce extracellular H 2 O 2 between transgenic AATP1(St) and wild-type potato tuber tissue, the release of H 2 O 2 from these two types of tissue was quantified. We first focused on tissues from wildtype and antisense line JT654 plants, because tubers from the latter show strong inhibition of starch biosynthesis and substantially altered levels of primary metabolites (Tjaden et al, 1998;Geigenberger et al, 2001).…”

“…antisense tubers are characterized by a decreased content of starch, increased levels of soluble sugars, and altered concentrations also of other intermediates of primary metabolism (Tjaden et al, 1998;Geigenberger et al, 2001). Here, we have shown that AATP1(St) antisense tuber tissue also displays improved capacity to activate various cellular defense responses but only upon treatment with elicitors, E. carotovora cells, or the E. carotovora culture supernatant ( Figs.…”

The Import and Export Business in Plastids: Transport Processes across the Inner Envelope Membrane

“…These transporters exert significant control on starch synthesis in amyloplasts of potato (Solanum tuberosum) tubers and on lipid biosynthesis in developing Arabidopsis seeds (Geigenberger et al, 2001).…”