Arabidopsis roots and shoots have different mechanisms for hypoxic stress tolerance

Abstract

Arabidopsis has inducible responses for tolerance of O2 deficiency. Plants previously exposed to 5% O2 were more tolerant than the controls to hypoxic stress (0.1% O2 for 48 h) in both roots and shoots, but hypoxic acclimation did not improve tolerance to anoxia (0% O2). The acclimation of shoots was not dependent on the roots: increased shoot tolerance was observed when the roots of the plants were removed. An adh (alcohol dehydrogenase) null mutant did not show acclimation of the roots but retained the shoot survival response. Abscisic acid treatment also differentiated the root and shoot responses; pretreatment induced root survival in hypoxic stress conditions (0.1% O2) but did not induce any increase in the survival of shoots. Cycloheximide blocked both root and shoot acclimation, indicating that both acclimation mechanisms are dependent on protein synthesis.

Figure 1

Survival of HPT and NHPT plants after various times of hypoxic stress (A) and anoxia (B). Error bars represent the se. In this experiment only the survival of the existing root tip was scored; growth from lateral roots was not recorded. When the survival of the root system as a whole was scored after 48 h of hypoxic stress, survival in the HPT plants was 100%.

Figure 2

Shoot survival of plants with roots (A), with roots removed before pretreatment (B), or with roots removed before treatment (C). The pretreatment is indicated on the x axis, and was followed by 48 h of hypoxic stress. Error bars represent the se.

Figure 3

Shoot survival (A), shoot chlorophyll content (B), root survival (C), and root fresh weight (FW) (D) of plants that were given the pretreatment shown on the x axis, and were then either exposed to 48 h of hypoxic stress or were aligned on the recovery plates without a stress. Plants were pretreated with hypoxia only (HPT), with hypoxia with cycloheximide in the liquid medium (1 μg mL⁻¹ cycloheximide [CX1-HPT] or 10 μg mL⁻¹ cycloheximide [CX10-HPT]), or were not pretreated (NHPT). Error bars represent the se.

Figure 4

Vertical recovery plates 2 weeks after a 48-h hypoxic stress treatment. Top left, NHPT Bensheim; top right, HPT Bensheim; bottom left, NHPT adh null mutant R002; and bottom right, HPT adh null mutant R002.

Figure 5

Recovery scores of Bensheim (Ben.) and the adh null mutant (R002), HPT, and NHPT (as indicated on the x axis) after 48 h of hypoxic stress. A, Shoot survival; B, shoot chlorophyll content; C, percentage of plants showing growth from the existing root; D, root fresh weight (FW). Error bars represent the se.

Figure 6

Recovery scores of plants that were given the pretreatment indicated on the x axis followed by 48 h of hypoxic stress. A, Shoot survival; B, shoot chlorophyll content; C, root survival; D, root fresh weight (FW). Error bars represent the se.