Plant Physiology Biochemistry

Step 1: Understand the Agrobacterium-mediated transformation process
Agrobacterium tumefaciens naturally transfers a segment of its DNA (T-DNA) into the plant genome, making it a useful tool in genetic engineering of plants.
Step 2: Identify the role of selection marker genes
In the laboratory, to ensure only the transformed cells survive and grow, selection marker genes (e.g., antibiotic or herbicide resistance genes) are inserted along with the gene of interest into the T-DNA. These allow preferential growth of successfully transformed cells.
Step 3: Eliminate incorrect statements
(1) is incorrect — the efficiency of transformation is often influenced by the genotype of the host plant.
(2) is incorrect — the T-DNA integration can be single or multiple copies.
(4) is incorrect — opine gene expression is not essential for transformation; it was more relevant in wild-type Agrobacterium interactions.

Step 1: Understand water movement in plants.
Water moves in plants primarily through processes like osmosis, transpiration pull, and root pressure. The direction of water movement depends on the water potential gradient.
Step 2: What is water potential?
Water potential ( ) is a measure of the potential energy of water in a system compared to pure water, and it determines the direction of water movement. Water always moves from a region of higher (less negative) water potential to a region of lower (more negative) water potential.
Step 3: Eliminate incorrect options.
Ionic potential refers to charge-based ion properties.
Membrane potential relates to charge difference across membranes, not water movement.
Soil temperature affects water absorption rate but is not the driving force.
Therefore, Water potential is the correct answer.