Soil Fertility as a Contingent Rather than Inherent Characteristic - Principles of Sustainable Soil Management in Agroecosystems - page 158

Using the criterion of at least a twofold change in the abundance of particular
proteins in the analyzed tissues, 21, 19, and 12 protein-expression spots were found
to have such large differentials displayed in the respective gel electrophoresis profiles
of samples from roots, leaf sheaths, and leaves.
These divergences are indicative of either up-regulation or down-regulation of
gene expression. According to their gene annotation in the database, the identified
proteins analyzed in the three sets of rice tissues could be classified into nine func-
tional groups. These groups are primary metabolism proteins, energy-associated
proteins, defense-related proteins, protein destination and storage agents, transport-
ers, signal transduction proteins, cell growth/division proteins, cell-structure pro-
teins, and unknown-function proteins (Figure 6.3).
All of the seven energy-associated proteins identified in the roots were down-
regulated by rhizobium inoculation, while most of the energy-associated proteins
identified in the leaf sheaths and leaves were up-regulated, as were the proteins asso-
ciated with the photosynthesis subgroup. In roots, all the up-regulated proteins were
classified as ones involved in signaling or as defense-related, whereas only two
defense-related proteins were identified in leaf sheaths.
Promotion of plant growth in response to rhizobial infection : Several proteins
produced in cell chloroplasts that contribute to photosynthesis enhancement in the
plant canopy were up-regulated in association with or in response to rhizobial colo-
nization. These photosynthesis-related proteins include

• Rubisco activase and pyruvate orthophosphate dikinase, which could

increase CO 2 -ixation efficiency.

100%

Unknown functions
Defense
Signal transduction
Cell structure
Transporters
Protein destination/storage
Cell growth/division
Energy associated
Metabolism

90%

80%

70%

60%

50%

40%

30%

20%

10%

0%

Root Leaf

sheath

Leaf

FIGURE 6.3 Functional categorization of the differentially expressed proteins in the root,
leaf sheath, and leaf tissues in rice plants resulting from inoculation with S. meliloti 1021.