Table 1. How abiotic and biotic environmental stresses influence hormone levels.

	Heat	Light	CO2	Drought	Flood	Resistance to biotrophs	Resistance to necrotrophs	Resistance to herbivores
Abscisic acid	increases [7]	increases [8]	increases [5]	increases [9]	reduces/increases [10]	reduces [11]	increases [11]	reduces/increases [12]
Auxin	reduces [7]	reduces [13]	increases [5]	reduces? [6]	reduces [14]	reduces [15]	increases [16]	species/tissue specific [12]
Brassinosteriods	increases [17]	reduces [13]	?	reduces [17]	reduces [14]	increases/reduces [18]	increases [18]	reduces [12]
Cytokinins	reduces [7]	increases [19]	increases [5]	reduces [19]	reduces [20]	increases/reduces [15]	increases [21,22]	increases [23]
Ethylene	increases [24]	reduces [8]	reduces [5]	increases [6]	increases [10]	reduces [25]	increases [26]	reduces/increases [12]
Gibberellins	reduces [7]	increases [13]	increases [27]	reduces [6]	reduces [10]	increases [28]	reduces [16]	reduces [12]
Strigolactones	increases [29]	increases [8]	?	reduces [6]/increases [29]	?	increases [30]	increases [31]	increases [32]

The table describes how hormone levels can generally be summarized to respond in plants in a range of environmental challenges. However, the responses will vary significantly depending on the specific type of interaction, e.g. plant/pathogen species, the tissue/organ type, stress intensity, and response timeframe examined. The first half of the table summarizes the phytohormone responses during five abiotic stresses. The second half of the table describes how hormones respond in general terms during immune responses induced by biotrophs, necrotrophs, and herbivore pests.