Treating water stress in plants

A method of increasing the yield of a drought stressed crop plant, the method comprising applying a compound to the plant, wherein the compound is of formula (I) or agriculturally acceptable salt thereof:

• wherein;
• p is 0 or 1;
• R1 to R7 independently represent F, N3, NR′R″, C1-4alkyl, —(C1-4alkyl)OH or OH, wherein R′ and R″ independently represent hydrogen or C1-4alkyl;
• and R8 and R9 are the same or different and represent H or a photo-labile protecting group, wherein at least one of R8 and R9 represents a photo-labile protecting group, and wherein the photo-labile protecting group is of formula (II):
• wherein;
• ring A is selected from the group consisting of a C6-10 aryl group, and a dibenzofuranyl ring, and further wherein the aryl group is unsubstituted or substituted with one or more substituents selected from C1-4 alkyl, —OR′, halogen, CN, —NR′R″, —COOR′, —(C1-4 alkyl)COOR′ and —O(C1-4 alkyl)COOR′, wherein R′ and R″ are independently selected from hydrogen and C1-4 alkyl or wherein two adjacent ring positions of the C6-10 aryl group are substituted with a —CH2—O—CH2 moiety;
• either (i) R10 and R11 are the same or different and are selected from hydrogen, C1-4alkyl which is unsubstituted or substituted with one or more halogen atoms, —OR′, halogen, —NR′R″ or —CO2R′, wherein R′ and R″ are independently selected from hydrogen and C1-4alkyl, or (ii) two R10 groups on adjacent photo-labile protecting groups together form a bond and R11 represents hydrogen, C1-4alkyl which is unsubstituted or substituted with one or more halogen atoms, —OR′, halogen, —NR′R″ or —CO2R′, wherein R′ and R″ are independently selected from hydrogen and C1-4alkyl;
• n is 0 or 1;
• and
• R12 and R13 are the same or different and are selected from hydrogen, C1-4alkyl which is unsubstituted or substituted with one or more halogen atoms, —OR′, halogen, —NR′R″ or —CO2R′, wherein R′ and R″ are independently selected from hydrogen and C1-4 alkyl;
• wherein X represents the link to the remainder of the compound of formula (I).