Interactions between Pseudomonas putida UW4 and Gigaspora rosea BEG9 and their consequences for the growth of cucumber under salt-stress conditions.
OBJECTIVE
After the determination of the toxic but nonlethal concentration of NaCl for cucumber, we examined the interaction between an ACC (1-aminocyclopropane-1-carboxylate) deaminase producing bacterial strain and an arbuscular mycorrhizal fungus (AMF) and their effects on cucumber growth under salinity.


RESULTS
In the first experiment, cucumber seedlings were exposed to 0.1, 50, 100 or 200 mmol l(-1) NaCl, and plant biomass and leaf area were measured. While seeds exposed to 200 mmol l(-1) NaCl did not germinate, plant growth and leaf size were reduced by 50 or 100 mmol l(-1) salt. The latter salt cancentration caused plant death in 1 month. In the second experiment, seeds were inoculated with the ACC deaminase-producing strain Pseudomonas putida UW4 (AcdS(+)), its mutant unable to produce the enzyme (AcdS(-)), or the AMF Gigaspora rosea BEG9, individually or in combination and exposed to 75 mmol l(-1) salt. Plant morphometric and root architectural parameters, mycorrhizal and bacterial colonization and the influence of each micro-organism on the photosynthetic efficiency were evaluated. The AcdS(+) strain or the AMF, inoculated alone, increased plant growth, affected root architecture and improved photosynthetic activity. Mycorrhizal colonization was inhibited by each bacterial strain.


CONCLUSIONS
Salinity negatively affects cucumber growth and health, but root colonization by ACC deaminase-producing bacteria or arbuscular mycorrhizal fungi can improve plant tolerance to such stressful condition.


CONCLUSIONS
Arbuscular mycorrhizal fungus and bacterial ACC deaminase may ameliorate plant growth under stressful conditions. It was previously shown that, under optimal growth conditions, Ps. putida UW4 AcdS(+) increases root colonization by Gi. rosea resulting in synergistic effects on cucumber growth. These results suggest that while in optimal conditions ACC deaminase is mainly involved in the bacteria/fungus interactions, while under stressful conditions this enzyme plays a role in plant/bacterium interactions. This finding is relevant from an ecological and an applicative point of view.
Gamalero
E
E
Università del Piemonte Orientale 'Amedeo Avogadro', Dipartimento di Scienze dell'Ambiente e della Vita, Viale Teresa Michel 11, Alessandria, Italy.
Berta
G
G
Massa
N
N
Glick
B R
BR
Lingua
G
G
D001426:Bacterial Proteins / Q000378:metabolism; D019755:Carbon-Carbon Lyases / Q000378:metabolism; D018553:Cucumis sativus / Q000382:microbiology*; D055137:Glomeromycota / Q000254:growth & development*; D038821:Mycorrhizae; D018515:Plant Leaves / Q000382:microbiology; D016958:Pseudomonas putida / Q000201:enzymology / Q000254:growth & development*; D036226:Seedlings / Q000382:microbiology*; D013312:Stress, Physiological
D001426:Bacterial Proteins; C033634:1-aminocyclopropane-1-carboxylate deaminase; D019755:Carbon-Carbon Lyases